Multi-Wavelength Observations of Coronal Structure and Dynamics -- Yohkoh 10th Anniversary Meeting |
Yohkoh10 Abstracts
| Presentor: | Sachiko Akiyama |
| Title: | Soft X-ray High-Temperature Regions above Solar Flare Loops |
| Authors: | Akiyama, S (Naval Research Laboratory)
Hara, H (National Astronomical Observatory of Japan) |
| We analyzed 141 solar flare data observed with the
{it Yohkoh} soft and hard X-ray telescopes to investigate general characteristics of soft X-ray high-temperature regions above flare loops. Although existence of the high-temperature region was first reported by Masuda et al. (1994), it has been criticized by several authors because the soft X-ray intensity of that region is weak and because it is usually located near a relatively large intensity gradient. A careful analysis is required for a systematic research that reveals general characteristics of the region and roles in the flare energy release mechanism. We carefully estimated the electron temperature of a flare site with the filter ratio technique from the {it Yohkoh} soft X-ray data under an isothermal approximation after correcting the spacecraft pointing jitter and scattered X-rays due to the mirror micro-roughness, both of which are causes of the criticism. We have still found the high-temperature regions of 15--35 million degrees above flare loops for 64 flares in 141 events. A single flare event had single/multiple high-temperature region of 1--3 imes 10$^{4}$ km in size. The region appeared at the hard X-ray impulsive phase and its temperature reached a maximum before the soft X-ray peak time. The volume emission measure of the region was 10$^{47--48}$ cm$^{3}$, which was about ten times smaller than that of 10 million degree flare loops beneath. The high-temperature regions tended to move outwards at a speed of 10--20 km s$^{-1}$, which was systematically faster than the rising speed of flare loops of 4--6 km s$^{-1}$. When the high-temperature regions were located in asymmetrical point to the two footpoints of flare loop, the regions were located at the side of a weaker hard X-ray source measured with the {it Yohkoh} hard X-ray telescope, showing that the high-temperature regions appear at the side of a footpoint with a weaker magnetic field than the other. | |
| Presentor: | David Alexander |
| Title: | Yohkoh: A Decade of Discovery |
| Authors: | Alexander, D (Lockheed Martin Solar and Astrophysics Lab.) |
| Data from the Yohkoh satellite has led the way in the dissemination of scientific knowledge to the general public over the last decade. This talk will discuss the role that solar physics in general, and Yohkoh in particular, have played in stimulating a public interest in science and the effect they have had in the teaching of science in the classroom. To highlight Yohkoh we will discuss the extremely successful Yohkoh Public Outreach Project and its daughter Solar Week with particular emphasis on the role played by scientists in the effective dissemination of the solar science. | |
| Presentor: | Richard Altrock |
| Title: | Long-Term Variation of the Rotation of the Solar Corona |
| Authors: | Altrock, R. C. (Air Force Research Laboratory, Space Vehicles Directorate) |
| Synoptic photoelectric observations of the coronal Fe XIV and Fe X
emission lines at 530.3 nm and 637.4 nm, respectively, are analyzed to study the rotational behavior of the solar corona as a function of latitude, height and time. The data used are measurements made with the Sacramento Peak 40-cm coronagraph and Emission-Line Coronal Photometer of the intensity of these lines observed at 1.15 to 1.45 solar radii (Ro) between 1973 (1984 for Fe X) and 2000. An earlier similar temporal-correlation analysis of the Fe XIV data at 1.15 Ro over only one 11-year solar activity cycle (Sime, Fisher and Altrock 1989, Astrophys. J. 336, 454) found suggestions of solar-cycle variations in the differential-rotation and latitude-averaged-rotation patterns that combined the effects of large-scale patterns seen in the white-light corona and smaller-scale patterns seen in chromospheric and photospheric rotation. These results will be tested over the longer epoch now available. In addition, the new 1.15 Ro Fe XIV results will be compared with those at greater heights and with results from the Fe X line and radio frequencies (Vats et al. 2001, Astrophys. J., 548, L87) to form a global picture of solar rotation throughout the corona and over more than two solar cycles. | |
| Presentor: | Ayumi Asai |
| Title: | Fine Structure inside Flare Ribbons and its Temporal Evolution |
| Authors: | Asai, A. (Kwasan Observatory, Kyoto University)
Masuda, S. (Solar-Terrestrial Environment Laboratory, Nagoya University) Yokoyama, T. (Nobeyama Radio Observatory /NAOJ) Shimojo, M. (Nobeyama Radio Observatory /NAOJ) Kurokawa, H. (Kwasan Observatory, Kyoto University) Ishii, T.T. (Kwasan Observatory, Kyoto University) Isobe, H. (Kwasan Observatory, Kyoto University) |
| Non-thermal particles generated in the impulsive phase of solar flares
are observed mainly in microwave, hard X-rays, and $gamma$-rays. Observations in H$alpha$ can also give important informations about non-thermal particles precipitating into the chromosphere with a higher spatial resolution than in other wavelengths. We observed an X2.3 flare which occurred in the active region NOAA 9415 on 10 April 2001, in H$alpha$ with Sartorius Telescope at Kwasan Observatory, Kyoto University. Thanks to the short exposure time given for the flare, the H$alpha$ images show fine structures inside the flare ribbons. In addition to H$alpha$, we analyze microwave, hard X-ray, and EUV data obtained with Nobeyama Radioheliograph, {it Yohkoh}/HXT, and TRACE, respectively. In H$alpha$, several bright kernels are observed in the flare ribbons. On the other hand, the hard X-ray images show only a single pair of bright sources which correspond to one of several pairs of H$alpha$ kernels. Examining the difference in the magnetic field strength and in the time profiles of H$alpha$ emission for these kernels, we discuss the reason why only one pair kernels are bright in the hard X-ray among the other bright H$alpha$ kernels. Comparing the H$alpha$ images with EUV images, we also examine the three-dimensional structure of solar flares. While broad and network-like ribbons are observed in H$alpha$, the width of EUV ribbons is relatively narrow, and EUV ribbons are located at the outer edges of the corresponding H$alpha$ ribbon. | |
| Presentor: | Markus Aschwanden |
| Title: | Reconciliation of the Coronal Heating Function between Yohkoh, SoHO, and TRACE |
| Authors: | Aschwanden, M.J. (Lockheed Martin, Solar and Astrophysics Lab.) |
| Mixed results on the determination of the coronal
heating function are quoted in literature. There seems to be a polarization between Yohkoh, SoHO/EIT, and TRACE results. Essentially, heating functions $E_H(s)$ derived from the temperature-broadband instrument SXT/Yohkoh yield best fits for uniform or looptop heating (Priest et al. 1998, 2000; Wheatland, Sturrock, & Acton 1997), while the same heating function derived from temperature-narrowband instruments like EIT and TRACE yield best fits for footpoint heating with scale heights of $s_H lapprox 15$ Mm. The problem seems to be rooted in oversimplified modeling of filter-ratio temperatures, using single-temperature models for every line-of-sight, although the broadband response of Yohkoh/SXT is sensitive to emission measure-weighted temperatures of the entire $dEM(T)/dT$ distribution above $T>1.5$ MK. We revisit previous analyses of Yohkoh data and demonstrate with forward-fitting methods of multi-temperature models or continuous $dEM(T)/dT$ distributions that both the Yohkoh/SXT and TRACE data can be reconciled, both yielding coronal heating function with scale heights of $s_H lapprox 15$ Mm, for active region loops as well as for quiet Sun region. This result has important consequences for the identification of the long-sought physical mechanisms responsible for coronal heating. | |
| Presentor: | Henry Aurass |
| Title: | Shock-excited Radio Burst from Reconnection Outflow JetNULL |
| Authors: | Aurass, H. (Astrophysikalisches Institut Potsdam, Germany)
Vrsnak, B. (University of Zagreb, Croatia) |
| Models of dynamic (two-ribbon-, arcade) flares involve the
formation of a system of standing slow and possibly also fast mode shock waves associated with the fast reconnection process below the erupting filament. These shocks are anticipated theoretically, but are not undoubtedly confirmed by observations. In this paper we identify for the first time the radio signature of a fast mode outflow termination shock in a dynamic radio burst spectrogram. The standing fast mode shock is revealed by a zero-drift type II burst recorded between 300 and 400 MHz. It started almost 1 hour after the impulsive phase of the 07 April 1997 flare and lasted for more than 30 min. The burst shows a characteristic herringbone fine structure and a band split of 10-20~\% of the emission frequency. No fundamental-harmonic pattern was observed, and we argue that the feature is fundamental mode emission. Simultaneous imaging observations (H$alpha$, {it Yohkoh} SXT, SOHO EIT) show a relaxed postflare loop arcade with a bright soft X-ray cusp commonly interpreted as a typical reconnection pattern. Conditions for termination shock formation and excitation of radio emision are investigated. Favourable circumstances for the radio detection of a termination shock in the reconnection outflow are a comparatively large height of the diffusion region, a low plasma to magnetic pressure ratio $eta$ upstream of the slow shocks, and a small angle between the reconnecting field lines. Finally, we discuss why similar radio signatures are not observed more frequently, and why it appeared so late in the event. We stress the implications and point to some inconsistencies which might be a consequence of commonly practiced {it ad hoc} implantation of idealized model results to realistic conditions. | |
| Presentor: | Dipankar Banerjee |
| Title: | Long Period Oscillations in Polar coronal holes as observed by CDS on SOHO |
| Authors: | Banerjee, D (Centre for Plasma
Astrophysics, Katholieke Universiteit Leuv)
O'Shea, E (ESA/ESTEC, Solar System Division, Keplerlaan 1, NL-2201 AZ, ) Doyle, J,G (Armagh Observatory, Armagh, BT61 9DG, N. Ireland) Goossens, M (Centre for Plasma Astrophysics, Katholieke Universiteit Leuv) |
| We examine spectral time series of the coronal line Mg~{\sc ix}~368 \AA , the transition region line O~{\sc v}~629 \AA, and the chromospheric line He~{\sc i}~584 \AA observed during several periods of 2000, with the Coronal Diagnostic Spectrometer (CDS) onboard the SoHO spacecraft. We study different parts of coronal holes, plumes and inter-plumes (off-limb) as a separate study. We report here on a time series analysis, using wavelet methods, of small individual regions in the polar coronal hole. The wavelet analysis allows us to derive the duration as well as the periods of the oscillations. The statistical significance of the oscillations was estimated by using a randomisation method. Our observations indicate the presence of compressional waves with periods of 20-30 minutes or longer. These slow magneto-acoustic waves may provide enough enrgy flux for the acceleration of the fast solar wind. | |
| Presentor: | Elena Benevolenskaya |
| Title: | Coronal Patterns of Activity from YOHKOH and SOHO/EIT Data |
| Authors: | Benevolenskaya, E.E. (Pulkovo Observatoty/Stanford University)
Kosovichev, A.G. (Stanford University) Lemen, J.R. (LMSAL) Slater, G.L. (LMSAL) |
| We have studied the evolution of large-scale coronal structures using soft X-ray data from YOHKOH and EUV data from SOHO/EIT during the rising phase of the current solar cycle 23, and compared with the evolution of the photospheric magnetic field. During this period the
distribution of the coronal structures generally reflects the evolution of the magnetic fields. However, the data from YOHKOH and EIT reveal large-scale magnetic connections in the corona that probably play significant role in the solar cycle. In particular, we have found that coronal structures such as high-latitude giant loops may be important for the topological evolution of magnetic structures during the solar cycle and for polar magnetic field reversals. We discuss possible mechanisms of the polar magnetic field reversals and their relations to the observed coronal structures. | |
| Presentor: | Jeffrey Brosius |
| Title: | Search for Evidence of Alpha Particle Beams During a Solar Flare |
| Authors: | Brosius, J., W. (Raytheon ITSS at NASA's GSFC) |
| We observed NOAA Region 9090 (N13 W39) with SOHO's CDS and EIT between 18:17 and 21:09 UT on 24 July 2000 to search for evidence of alpha particle beams during solar flares. The GOES satellite reports a C3.8 event in this region from 19:57 to 20:05 UT. Theoretically, an alpha particle beam will manifest itself during the impulsive phase of a flare through an enhancement in the red wing of the He II Ly$\alpha$ (303.782 \AA) emission line, without a corresponding blue wing enhancement. This enhancement is due to downstreaming nonthermal alpha particles undergoing charge exchange with chromospheric neutral hydrogen atoms to form downstreaming nonthermal He II ions. Ly$\alpha$ radiation emitted from these downstreaming ions is Doppler-shifted into the red wing of the Ly$\alpha$ line. Our CDS observing program acquired high time resolution (9.7 s) $4''\times 4'$ slit spectra between 590 and 630 \AA, where we observed He II Ly$\alpha$ in second order (607.564 \AA). We fit the spectral background and emission line profiles for each CDS spectrum in our observed sequence. Density- and temperature-insensitive intensity ratios of O IV and Mg X lines generally agree with their theoretical values before and after the flare, but differ significantly from their theoretical values during the flare. This may indicate line blending with unknown components, line blending with second order C IV and Fe XV lines, or loss of ionization equilibrium. Most important, however, we find that although the red wing and blue wing backgrounds for He II Ly$\alpha$ remain relatively constant during most of our observation, the blue wing undergoes a more significant enhancement during the flare than does the red wing. This effect is opposite that expected in the presence of an alpha particle beam. Further, blended spectral line features that mimic the expected nonthermal redshifted He II Ly$\alpha$ beam signal are understood in terms of well known emission line components. Thus we find no evidence for the presence of alpha particle beams in this case. | |
| Presentor: | Richard Canfield |
| Title: | Preflare Phenomena in Eruptive Flares |
| Authors: | Colman, A. M. (Physics Department, Montana State University)
Canfield, R. C. (Physics Department, Montana State University) Lamb, D. A. (Physics Department, Drake University) |
| We report the results of an observational study of preflare
dynamic signatures of magnetic reconnection events seen in H-alpha imaging spectra from Mees Solar Observatory. We studied an unbiased set of 16 events for which we have observations for several hours prior to the flare, some of which were eruptive and some not. The average rate of reconnection-event signatures was five times greater prior to the eruptive flares than the non-eruptive ones. Also, the rate of the reconnection event signatures was six times higher prior to the eruptive flares than after them. We have studied two of these active regions for several days prior to the flares of interest. In both regions, rates of reconnection-event occurence comparable to those near to flare time obtained during these several-day periods. Since these phenomena were seen in H-alpha, we believe that magnetic reconnection in the lower solar atmosphere plays a causal role in solar flare eruptions. | |
| Presentor: | Jonathan Cirtain |
| Title: | Isothermal Approximation vs. Differential Emission Measure Analysis: How Hot are Hot Loops? |
| Authors: | Cirtain, J, W (University of Memphis)
Schmelz, J, T (University of Memphis) |
| Analysis of EUV data from both EIT and TRACE suggests that active region loops may be isothermal. These results are in sharp contrast to the multi-thermal loops obtained from the analysis of X-ray data from SXT. The analysis of all these observations uses an isothermal approximation, but the EUV results are derived from narrow-band filter ratios while the X-ray results use a broad-band ratio. We have incorporated CDS data into the mix in two different ways: (a) we have used an isothermal approximation with different iron line ratios to determine temperatures at various pixels along a couple of (relatively) isolated coronal loops on the limb; and (b) we have used multiple spectral lines from the same data sets to produce differential emission measure distributions at these pixels. The data sets were obtained from observations taken on 13 Nov 1997 and 20 Apr 1998 by both CDS and SXT. We find that different instruments and/or different methods of analysis give different results. In some sense, this is not surprising since the limitations of the isothermal approximation are well understood. What is surprising, however, is that we sometimes forget these limitations. | |
| Presentor: | Emilia Correia |
| Title: | Dynamics of the corona magnetic field inferred from multi-frequency observations for the 1998 November 5 solar flare |
| Authors: | Correia, E. (CRAAE/INPE-CRAAM/IPM)
Raulin, J-P. (NONE) Trottet, G. (NONE) Kaufmann, P. (NONE) |
| We report multi-frequency observations of a solar GOES M1.5 class flare, occurred November 5, 1998 at about 1335 UT. The microwave observations were obtained by the Solar Radio Polarimeter at 7 GHz (Itapetinga/Brazil) with high sensitivity and time resolution. The 2D decimetric-metric radio images were made with Nancay Radio Heliograph. The hard X ray data are from BATSE/CGRO and HXT from YOHKOH. Radio spectral information was obtained from RSTN data. Thus, the event was observed over a wide range of altitudes, between the low corona where ~ 200 keV hard X rays from non-thermal electrons are produced, up to about 0.5 Ro, where the electron beams propagated outward. We discuss these observations in terms of the relation between the production of non-thermal eletctrons in the low /middle solar atmosphere and the dynamics of the high corona magnetic field traced by spatially resolved dm/metric emitting sources. The analysis of the 2D metric/decimetric images, associated to the fast structures in the time profiles at 7 GHz and hard X rays suggests a very complex magnetic configuration during the flare evolution. The results suggest the presence of various emitting sources at high altitudes, probably associated to different injections of non-thermal electrons. There is a suggestion that the energy release could start in the high corona by the interaction of large scale magnetic loops. | |
| Presentor: | Steven Cranmer |
| Title: | Coronal Holes and the Solar Wind |
| Authors: | Cranmer, S. R. (SAO) |
| Coronal holes are the darkest regions of the ultraviolet
and X-ray Sun, both on the disk and away from the limb. Coronal holes are associated with rapidly expanding open magnetic fields and the acceleration of the high-speed solar wind. This presentation will review measurements of the plasma properties of coronal holes and how these measurements have been used to put constraints on theoretical models of coronal heating and solar wind acceleration. Heat deposition at the dense and collisional coronal base is of comparable importance (in determining, e.g., temperature gradients and asymptotic outflow speeds) as extended heating in the collisionless regions above 2 solar radii. Thus, a complete understanding of the physics requires both observations of the solar disk and inner corona (Yohkoh, EIT, CDS, SUMER) and coronagraphic observations of the wind's acceleration region (UVCS, LASCO). Although strong evidence has been found to suggest that the high-speed wind is driven mainly by proton pressure, the differences between proton, electron, and heavy ion velocity distributions are extremely valuable as probes of the dominant physical processes. | |
| Presentor: | J. Len Culhane |
| Title: | Flare Characteristics and the Association with Ejective or Non-ejective Behaviour |
| Authors: | Culhane, J.L. (MSSL)
Matthews, S.A. (MSSL) Green, L.M. (MSSL) Magee, H.M. (MSSL) Harra, L.K. (MSSL) Foley, C.A. (MSSL) |
| The relationship between the characteristics of Solar Flares e.g. magnetic morphology, intensity, duration, and their association with ejective or non-ejective behaviour is discussed. One major example, which illustrates the association of non-ejective behaviour with magnetic topology in the case of a large (X 1.2) flare, is presented. Results of a statistical study of a sample of 104 flare events ranging from GOES class A up to class X are presented. The dependence of the flare/CME association on the intensity and duration of the flares is discussed. Based on results from a sample of 12 stellar X-ray flares, the implications of this work for our understanding of the nature of flares in late-type stars are also investigated. | |
| Presentor: | Alisdair Davey |
| Title: | The Yohkoh Archive at Montana State University |
| Authors: | Davey, A.R. (Montana State University) |
| MSU recently brought online 2.1 Tb of storage with a primary aim of providing space for work on the new Yohkoh movie. In the process, we have also been able to create another complete archive of Yohkoh data. We are investigating ways to make this data available to the community, that seek to maximize the scientific potential and make it easier for users to identify data of interest. In the first stage of the work, we will be providing an interface to integrated SXT / HXT Yohkoh data, which will build on the Yohkoh flare archive work of Jun Sato. | |
| Presentor: | Craig DeForest |
| Title: | Observing Small-Scale Coronal Heating: What's Next? |
| Authors: | DeForest, C.E. (Southwest Research Institute)
Parnell, C.E. (St. Andrews University) |
| The coronal heat remains mysterious. The currently fashionable theory is that small-scale reconnection in the ``magnetic carpet'' produces the heat stochastically. Many studies have associated magnetic flux at the photosphere with heating in the corona; but little is known about the coupling between specific flux motions and coronal heating events. We will present some recent results on the magnetic origin of polar plumes, simple structures that are representative of the quiet corona as a whole, and discuss what observations are required to resolve current outstanding questions. | |
| Presentor: | Danuta Dobrzycka |
| Title: | Ultraviolet and Soft X-ray polar coronal jets |
| Authors: | Dobrzycka, D. (Harvard-Smithsonian Center for Astrophysics)
Raymond, J. C. (Harvard-Smithsonian Center for Astrophysics) Cranmer, S. R. (Harvard-Smithsonian Center for Astrophysics) Li, J. (Institute for Astronomy) |
| Coronal jets are spectacular dynamic events originating
from different structures in the lower solar corona. Various jet--like phenomena were observed by Yohkoh's soft X--ray telescope (SXT) as well as instruments aboard SOHO. The relation among the different types of jets is still not yet clear. The Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) provided us with spectroscopy of polar coronal jets originating near flaring ultraviolet bright points within polar coronal holes. The very same points also appeared very bright in the SXT data. UVCS recorded the polar coronal jets as a significant enhancement in the integrated intensities of the strongest coronal emission lines: mainly H~I Ly$alpha$ and O~VI $lambdalambda 1032,1037$. Most of the detected jets were correlated with EIT Fe~XII 195~AA and LASCO C2 white-light events. Our modeling of the jet's observable properties provided estimates of the jet plasma conditions, as well as the initial electron temperature and heating rate required to reproduce the observed O~VI ionization state. We present results of the coordinated SXT and UVCS observations of the polar jets in December 1996. We discuss possible relation between the ultraviolet and X--ray events, compare their properties and consider the magnetic reconnection models, developed for X--ray jets, as a model for UV jet formation. This work is supported by the National Aeronautics and Space Administration under grant NAG5--10093 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana, and by the ESA PRODEX program (Swiss contribution). | |
| Presentor: | Gordon Emslie |
| Title: | Scientific Results from HESSI - a Preview |
| Authors: | Emslie, A.G. (The University of Alabama in Huntsville) |
| The HESSI spacecraft is currently scheduled for a late
2001 launch. The instrument represents a quantum advance in our ability to analyze physical processes on spatial and temporal scales of physical interest, and to perform true spectroscopy on an astrophysical source. In this ``forward-looking review,'' I will discuss some of the exciting scientific investigations that HESSI will enable us to pursue. | |
| Presentor: | Gordon Emslie |
| Title: | HESSI Studies of Electron Transport in Solar Flares |
| Authors: | Emslie, A.G. (UAH) |
| We report on early results of spatially resolved hard X-ray
spectra from HESSI and their implications for models of electron acceleration and transport in solar flares. We discuss the inversion of the hard X-ray bremsstrahlung spectra to obtain electron flux spectra at different points in the source, and then the application of electron flux continuity to obtain empirical energy loss rates as a function of electron energy. Comparison will be made between the energy loss rates deduced from observations and those of different electron acceleration and transport models. | |
| Presentor: | David Falconer |
| Title: | Use of Yohkoh SXT in Measuring the Net Current and CME Productivity of Active Regions |
| Authors: | Falconer, D.A (UAH/MSFC)
Moore, R.L. (NASA/MSFC) Gary, G.A. (NASA/MSFC) |
| In our investigation of the correlation of global nonpotentiality of active regions to their CME productivity (Falconer, D.A. 2001, JGR, in press, and Falconer, Moore, & Gary, 2000, EOS 82, 20 S323), we use Yohkoh SXT images for two purposes. The first use is to help resolve the 180$^{o}$ ambiguity in the direction of the observed transverse magnetic field. Resolution of the 180$^{o}$ ambiguity is important, since the net current, one of our measures of global nonpotentiality, is derived from integrating the dot product of the transverse field around a contour ($I_{N}=\int B_{T}\cdot dl$). The ambiguity results from the observed transverse field being determined from the linear polarization, which gives the plane of the direction, but leaves a 180$^{o}$ ambiguity. Automated methods to resolve the ambiguity ranging from the simple acute angle rule (Falconer, D.A. 2001) to the more sophisticated annealing method (Metcalf T.R. 1994). For many active regions, especially ones that are nearly potential these methods work well. But for very nonpotential active regions where the shear angle (the angle between the observed and potential transverse field) is near 90$^{o}$ throughout large swaths along the main neutral line, both methods can resolve the ambiguity incorrectly for long segments of the neutral line. By determining from coronal images, such as those from Yohkoh/SXT, the sense of shear along the main neutral line in the active region, these cases can be identified and corrected by a modification of the acute angle rule described here. The second use of Yohkoh/SXT in this study is to check for the cusped coronal arcades of long-duration eruptive flares. This signature is an excellent proxy for CMEs, and was used by Canfield, Hudson, and McKenzie (1999 GRL V26, 6, 627-630). This work is funded by NSF through the Space Weather Program and by NASA through the Solar Physics Supporting Research and Technology Program. | |
| Presentor: | Frantisek FARNIK |
| Title: | X-Ray Jets in Interconnecting Loops |
| Authors: | SVESTKA, Z. (CASS, UCSD La Jolla and SRON Utrecht)
FARNIK, F. (Astronomical Institute Ondrejov) |
| We present several examples of X-ray jets, observed by the SXT onboard Yohkoh, which followed trajectories of transequatorial interconnecting loops (TILs). All these TILs were preexisting, seen some time before, but mostly invisible at the time of the onset of the jet which often made them bright along their total length. With few exceptions, these TIL-associated jets have properties very similar to other jets ejected inside active regions or along open field lines (footpoints in X-ray bright points, recurrence, strong collimation, average speed between 340 and 380 km s-1, but may reach very large lengths, in excess of 450 000 km. Exceptions are one jet that moved slower and one that had no brightened area at its source region at the time of its origin (an X-ray bright point appeared there only 3 hours later). It appears that less than 20% of X-ray jets are of this kind. | |
| Presentor: | Frantisek FARNIK |
| Title: | Current-Loop Coalescence Model Applied on the 7 April 1997 Flare |
| Authors: | FARNIK, F. (Astronomical Institute Ondrejov)
KARLICKY, M. (Astronomical Institute Ondrejov) |
| Very regular time variations of the 3 GHz radio flux observed during the 7 April 1997 flare are presented together with Yohkoh-SXT and SOHO-EIT observations. On lower frequencies (40-800 MHz) the variations were followed by several branches of type II radio burst. In the post-maximum phase of this flare the Yohkoh images indicate I-type of the flare loop interaction. The observations were analyzed and it was found that the data can be described by the current-loop coalescence model: the main period of the 3 GHz radio flux (about 100 s) corresponds to the repetition of the current-loop coalescence, and the radio double-peaks are associated with the maximum of the electric field component perpendicular to the interaction plane. The plasma beta-parameter in the current-loop coalescence process was estimated as 0.63. Indications of the beta-parameter increase during the flare are found. | |
| Presentor: | Andrzej Fludra |
| Title: | EUV Emission and the Magnetic Field in Active Regions |
| Authors: | Fludra, A. (Rutherford Appleton Laboratory, UK)
Ireland, J. (NASA Goddard Space Flight Center) |
| Relationships between the photospheric magnetic flux and
intensities of spectral lines emitted from the solar atmosphere have been extensively studied by several authors. Power-law relations have been found between the total magnetic flux and total intensities of the chromospheric, transition region and coronal emission lines in active regions. We address this topic and extend the previous work by using Extreme Ultraviolet lines recorded by the Coronal Diagnostic Spectrometer on SOHO for 50 solar active regions, as they crossed the central meridian in years 1996-1998. We use four spectral lines: He~I 584.3 AA ($2 imes 10^4$~K), O~V 629.7 AA ($2.2 imes 10^5$~K), Mg~IX 368.06 AA ($9.5 imes 10^5$~K), and Fe~XVI 360 AA ($2.0 imes 10^6$~K). None of these lines has been used before for this analysis. In particular, the Fe~XVI 360 AA line, seen only in areas of enhanced heating in active regions or bright points, is found to be a good indicator of the coronal heating. We establish empirical relations among intensities of those four lines, and between the total active region line intensity and the total magnetic flux. The dependence of the coronal loop heating rate on the magnetic flux density is derived and its implications for the coronal heating models are discussed. | |
| Presentor: | Carl Foley |
| Title: | What are the Origin of Quiescent Coronal Soft X-rays |
| Authors: | Foley, C.R. (Mullard Space Science Laboratory, UK)
MacKay, D. (St Andrews University, Scotland, UK) Yurow, R (Emergent IT, USA) Culhane, J.L. (Mullard Space Science Laboratory, UK) |
| We have examined the evolution and modulation of the Sun's
atmosphere from the photosphere up to the outer corona through the decline and rise of solar cycles 22, and 23 respectfully. For this we have used Yohkoh soft X-ray telescope (SXT) images, Kitt peak magnetograms and EUV spectra provided by the Coronal Diagnotic Spectrometer (CDS). We find as Hara (1996, 1997) found, that there is a modulation of the coronal brightness which varies annually in the high lattitude activity zones, and that this is linked to the presence and disappearence of active regions on the sun's disk. We interpret our results with regards to the emergence and diffusion of magnetic flux. We find that the appearence of high lattitude activity zones may be explained simply by the decay of diffused active region flux, We also find evidence for a positive temperature gradient within the corona from the emission profiles in the different lines. {References : Hara 1997, Advances in Space Research, 20, 12 ; Hara 1996, PhD thesis, Univerity of Tokyo } | |
| Presentor: | Carl Foley |
| Title: | Anatomy of a Flare and Coronal Mass Injection |
| Authors: | Foley, C, R (MSSL)
Harra, L, H (MSSL) Culhane, J, L (MSSL) Hori, K (MSSL) Matthews, S, A (MSSL) |
| In this paper we present the observations of a flare, CME and their interaction obtained with the SOHO, Trace, and Yohkoh spacecraft. More specifically we show evidence for wave-like motions in the Trace 171 observations, of comparable speed to those usually inferred from EIT observations and thus termed `EIT waves'. We find that these waves commence at the same time at which a prominence is observed to rise within the active region and signifies the start of a gradual coronal mass ejection.
The prominence is observed with the Coronal Diagnostic Spectrometer, on SOHO, with red and blueshifts which can only be reconciled if the structure is rotating close to the plane of the image with an angle of $sim 72^o$, to line of sight. During, the impulsive phase of the flare the prominence and CME is observed to accelerate from 190km/s to 900km/s. | |
| Presentor: | Szymon Gburek |
| Title: | Blind deconvolution of the SXT PSF core part |
| Authors: | Szymon Gburek, SG (Space Research Centre, Polish Academy of Sciences, Solar Phy)
Janusz Sylwester, JS (Space Research Centre, Polish Academy of Sciences, Solar Phy) Petrus Martens, PM (Montana State University) |
| We show the first results of blind iterative deconvolution (BID) of the core part of SXT point spread function from flare images. As the performance and speed of BID algorithms depend on good initial guess for PSF function shape and quality of data used, we took special care of the data selection and processing. From the analysis of several compact flare kernels we came to conclusion that a good guess for PSF can be provided directly from images of X-ray compact structures observed by SXT. Next, we conducted extensive mission-long searches for compact structures through entire database of SXT full resolution frames.
The searches returned plenty compact structures which may be used for BID restoration purposes. The period of data selection has been then constrained to the year 2000. A period relatively short in comparison with Yohkoh mission duration but long enough to ensure good SXT CCD data coverage. Also optical transfer functions for the all compacts of 2000 found have been tested for their signal value distribution. Using observation for this selected set of structures we construct constraints for Al12 PSF shrouds and compare them with ground calibration data. | |
| Presentor: | Masaoki Hagino |
| Title: | Hemispheric Helicity Asymmetry in Active Regions for Solar Cycles 21-23 |
| Authors: | Masaoki Hagino, M (Meisei University)
Takashi Sakurai, T (National Astronomical Observatory of Japan) |
| Magnetic helicity observed at the surface carries information on the
invisible, sub-surface processes such as internal rotation and the behavior of magnetic flux tubes in the convection zone. It has been recognized that magnetic helicity shows a hemispheric rule; the northern (southern) hemisphere tends to show negative (positive) helicity. It is also known that this rule does not change with solar cycle. In order to further investigate these properties of helicity,we here analyzed our own data set covering 18 years and compared them with results from other observatories. We analyzed vector magnetograms in the period of 1983--2000 obtained with the Solar Flare Telescope(SFT:Mitaka) and the 65cm Solar telescope(OAO:Okayama) at the National Astronomical Observatory of Japan. The current helicity was determined by two methods for 180 active regions(SFT) and 430 regions(OAO). The first method calculates the electric currents over active regions by a direct differentiation and then evaluates the average helicity, $ alpha =frac {sum ( abla imes vec{B})_z cdot { m sign} (B_z)}{sum B_z} $. The second method uses the fitting of the linear force-free field $vec{B}_{ m cal}( alpha )$ to the observed transverse field $vec{B}_{ m obs}$ and finds the best-fit $alpha$ which minimizes $ frac{ sum [vec{B}_{ m cal}( alpha ) - vec{B}_{ m obs}]^2} {sum B_{ m obs}^2} $. We plotted the helicity against latitude($ heta$) and calculated a linear fit to the data. The slopes(${ m d}alpha /{ m d} heta$) of the fit obtained from the first and the second methods using the dataset from the SFT are $( -1.08 pm 0.51) imes 10^{-10} { m m}^{-1} { m deg}^{-1}$ and $ (-3.30 pm 1.14) imes 10^{-10} { m m}^{-1} { m deg}^{-1}$, respectively. From the data set of OAO only in the solar maximum phase (1983 and 1989-1992), we found the slopes $( -1.08 pm 0.51) imes 10^{-10} { m m}^{-1} { m deg}^{-1}$ and $ (-1.06 pm 1.04) imes 10^{-10} { m m}^{-1} { m deg}^{-1}$. Our results agree with the previous studies and confirm the hemispheric rule. Although errors are large, there is indication of time variability in helicity. The hemispheric rule ${ m d} alpha / { m d} heta < 0$ may not hold in some phase of the activity cycle. | |
| Presentor: | Yoichiro Hanaoka |
| Title: | High-speed H-alpha Camera for Solar Flare Observations |
| Authors: | Hanaoka, Y. (National Astronomical Observatory of Japan)
Noguchi, M. (National Astronomical Observatory of Japan) Ichimoto, K. (National Astronomical Observatory of Japan) Sakurai, T. (National Astronomical Observatory of Japan) |
| To resolve individual spikes (elementary bursts) of impulsive solar
flares requires a time resolution within 1 sec and a spatial resolution of about 1 arcsec. However, it is difficult to realize such high temporal and high spatial resolutions simultaneously with the hard X-ray instruments such as the HXT of Yohkoh and HESSI. On the other hand, it is easy to obtain one-arcsec resolution images with the video rate in the H-alpha flare observations. Therefore, the H-alpha observations are essentially important to study impulsive flares. The observations with such high resolutions produce huge amount of data. It was difficult to handle such a flood of data, but the recent advance of the computer technology enable us to handle vast data with a small computer. We have developed a new digital imaging system for the H-alpha imager of the Flare Telescope at Mitaka, NAOJ, for the high-cadence observations of the solar flares. It covers a 6x4.5 arcmin field of view with 660x494 pixels, and the time resolution is 1/30 sec at best (depending on the field of view). Initial observational results will be presented at the conference, and we hope to collaborate with HESSI and Yohkoh to observe energetic phenomena of the solar flares. | |
| Presentor: | Hirohisa Hara |
| Title: | Changes of Coronal Structures over the 11-year Solar Cycle |
| Authors: | Hara, H. (National Astronomical Observatory, Japan) |
| A single 11-year solar activity cycle is going to be covered by the {\it Yohkoh} observations that have started since 1991. In this paper the changes of coronal structures over the solar activity cycle, based upon the {\it Yohkoh} SXT observations, are reviewed, referring to previous observations which lead to important concepts for the origin of the solar activity and comparing with recent observations of the photosphere and corona by the other satellites. | |
| Presentor: | Louise Harra |
| Title: | Non-thermal velocities in flares |
| Authors: | Harra, L.K. (Mullard Space Science Laboratory, University College London) |
| The high resolution spectroscopic information from the Bragg Crystal Spectrometer onboard Yohkoh has provided us with new and exciting information about flares and active regions. In particular, there has been much work on understanding the excess line broadening above the thermal width (known as non-thermal line broadening). We have been able to look for the first time spectroscopically at the preflare stages. The timings of the non-thermal velocity relative to the hard X-ray emission has been investigated. Non-thermal velocities have been observed to increase ten minutes before the main flares begins. Progress has been made to locate the region of dominant non-thermal velocity. This is difficult due to the lack of spatial resolution. A discussion will be made on what can be expected from the EUV Imaging Spectrometer onboard Solar B, which combines both high spatial and spectral resolution simultaneously. | |
| Presentor: | Donald Hassler |
| Title: | The Need for High Time Resolution Imaging Spectroscopy |
| Authors: | Hassler, D.M. (Soutwest Research Institute) |
| While multi-thermal imaging is well addressed, and accepted as crucial to understanding the dynamic behavior of the Sun, time-resolved spectroscopic imaging has been largely omitted. High cadence image sequences of large reconnective events demonstrate clearly the associated changes in morphology and hint at plasma motions associated with the events; but because of ambiguities between thermal and density changes in the plasma, and between proper motion and successive illumination of visible features, images cannot by themselves capture the nature of the field-matter interaction. In the future, simultaneous spectroscopy and multi-thermal imaging at high time cadence will be essential to removing interpretational ambiguities and bringing scientific closure to the high resolution dynamic motions seen with Yohkoh, SOHO, and TRACE. With a fast optical design, optimized wavelength selection, and reliable scan mechanisms that are specifically designed for rapid, repetitive motions, it is possible to attain an order-of-magnitude jump in time resolution compared to existing EUV spectrometers, and achieve the high time cadence observations necessary to resolve these outstanding questions. | |
| Presentor: | Tadashi Hirayama |
| Title: | Solar Wind Acceleration, Mass Flux, and Boundary Conditions |
| Authors: | Hirayama, T. (Meisei University) |
| We propose that heating and acceleration of the solar wind are controlled by damping of the supra-thermal electron beams resulting from the unipolar induction of the twisting flux tubes. Damping length is found to be a fraction of the solar radius, and inversely proportional to the pressure in accord with Withbroe(1988).
We claim that the mass flux of the solar wind is determined by the evaporation up flow in the base of the transition region due to the excess heating of the corona as in flares, both in open fields and closed fields. We claim that to find the solar wind solution it is only necessary to give the conditions on and near the Sun, namely the energy flux of the twisting tube, evaporation mass flux and non-radial area expansion function. This should, ein principlef, be done without considering the interstellar condition or the passage of the critical point, because of the impossibility of sending information back to the Sun, and rapid change of the magnetic field originating faculae. | |
| Presentor: | Shigenobu Hirose |
| Title: | Models of Arcade Flares in View of Observations by Yohkoh, SoHO/EIT, and TRACE |
| Authors: | Hirose, S. (Science University of Tokyo)
Uchida, Y. (Science University of Tokyo) |
| Arcade formations in the arcade-type energy release phonomena suggest that there occur magnetic reconnections above the flaring arcades. On the other hand, dark filaments which suddenly erupt should play an important role in the energy release. Therefore a global model should explain the relationship between the dark filament eruption and the arcade flare in a consistent way. The idea that the dark filament is supported at the top of a simple loop and the magnetic reconnection occurs at the current sheet which is formed by the dark filament rise itself has been assumed in the "classical" model. But this model does not explain where the energy of the dark filament rise that breaks up the magnetic arcade comes from, and how the dark filament is supported at the top of a convex loop in a consistent way. Recent observations by Yohkoh, SoHO/EIT, and TRACE have revealed the magnetic configurations arround dark filaments before the energy release, and suggest that the dark filament is supported in the neutral sheet between two magnetic loop systems with longitudinal magnetic field component along them, rather than supported on the top of a simple magnetic arcade. This fact is consistent with the quadruple magnetic source model of the dark filament. In the latter model, the strong part of the bipolar connections is opened up by the effect of the opposite polarity-pair of magnetic regions, and a current sheet exists before the event, in clear contrast to the "classical" model. The quadruple source model can explain the thin partition-type shape of dark filaments, and the presence of the barbs for the first time. MHD simulations based on this model show that the dark filament prevents the magnetic reconnection between the two magnetic loop systems until destabilized. As it is expelled out, the magnetic reconnection becomes possible, and the rise of the dark filament is accelerated upwards by the flood of upcoming magnetic flux through magnetic reconnection. These results of simulations can explain key observational features in very natural ways. | |
| Presentor: | Gordon Holman |
| Title: | Theoretical Model Images and Spectra for Comparison with HESSI and Microwave Observations of Solar Flares |
| Authors: | Holman, G. D. (NASA/GSFC)
Sui, L. (CUA & NASA/GSFC) McTiernan, J. M. (UCB) Petrosian, V. (Stanford U.) |
| We have computed bremsstrahlung and gyrosynchrotron images and spectra from a model flare loop. Electrons with a power-law energy distribution are continuously injected at the top of a simi-circular magnetic loop. The Fokker-Planck equation is integrated to obtain the steady-state electron distribution throughout the loop. Coulomb scattering and energy losses and magnetic mirroring are included in the model. The resulting electron distributions are used to compute the radiative emissions. Sample images and spectra are presented.
We are developing these models for the interpretation of HESSI x-ray/gamma-ray data and coordinated microwave observations. The Fokker-Planck and radiation codes are available on the Web at http://hesperia.gsfc.nasa.gov/hessi/modelware.htm This work is supported in part by the NASA Sun-Earth Connection Program. | |
| Presentor: | Kuniko Hori |
| Title: | Trajectories of micorwave prominence eruptions |
| Authors: | Hori, K. (NASA MSFC/NSSTC/NRC)
Culhane, J.L. (MSSL) |
| We examine the trajectories of 50 prominence eruptions observed in microwave continuum emission near solar maximum (1999-2000). On the basis of Nobeyama Radioheliograph 17 GHz images, we address two major questions; i) what triggers the prominence activity, and ii) how does the prominence motion affect or reflect the surrounding coronal structures. We found that most prominence activity is related to some weak energy release (or heating) taking place in the lower corona as suggested by the increase of the brightness temperature. By combining the 17 GHz prominence images with white-light synoptic maps from the LASCO C2 coronagraph on the {\it SOHO} spacecraft, we verify that 94 $\%$ of the prominence eruptions were associated with coronal mass ejections (CMEs) and that the remaining 6 $\%$ show weak mass motions confined to streamers. We confirm that coronal mass motions involving prominence eruptions and CMEs are not random but are organized by bundles of streamers. The large scale evolution of coronal features within 4.5 solar radii suggests that streamers are a signature of multiple plasma sheets emanating from active region belts, arcades, trans-equatorial interconnecting loops, and polar crown filaments, through which coronal mass is transported toward interplanetary space. This implies that magnetic forces exerted by streamers (or plasma sheets) play an important role in driving transient mass motions away from the Sun, against solar gravity. | |
| Presentor: | Kuniko Hori |
| Title: | Tether-cutting action in two sigmoidal filaments |
| Authors: | Hori, K (NASA MSFC/NSSTC/NRC)
Alexi, G. (Mullard Space Science Laboratory) Akioka, M. (Communications Research Laboratory) Ueno, S. (Hida Observatory) |
| The impressive S (or inverse-S) mark appearing on the lower corona, called sigmoid, is known as the manifestation of highly sheared magnetic structures (Rust and Kumar 1996). Recent studies using Yohkoh Soft X-ray Telescope (SXT; Tsuneta et al. 1991) has indicated that soft X-ray sigmoids, i.e., hot (\ge 2MK) S-shaped features, are strongly linked with eruptive phenomena, such as filament eruptions, flares, and coronal mass ejections (CMEs) (Sterling and Hudson 1997 Hudson et al. 1998; Canfield et al. 1999). However, previous papers have focused on the magnetic topology (e.g., helicity, shear buildup) of the sigmoid and connection with the resultant CME (e.g., missing mass deduced from dimming), and thus the physical process involved in the sigmoid formation and eruption is still not well addressed (e.g., van Driel-Gesztelyi et al. 2000). In this paper, we present observations of two sigmoidal filaments, in which development of the cool (\sim 10^4 K) sigmoids was well resolved with the high-cadence H alpha and microwave images (\le 30 sec). One is an active region filament and the other is a quiet region filament, whose long term evolution was reported by Glover et al. (2001). Both filaments were overlying the magnetic neutral line and their activities were associated with GOES B class flares. Comparison of SXT images and H alpha images illustrates that each filament almost coincides with a soft X-ray long structure that is apparently consisted of two short loops. The key features commonly observed in these filaments can be summarized as follows: i) The initial activity (small brightening) started at the middle of the sigmoidal filament. ii) The activity propagated upward crossing the filament at the junction of the two soft X-ray short loops, suggesting the so-called "tether-cutting" action (Sturrock 1989; Moore and Roumelios 1992). After the flare, the active region filament extended northward and formed an inverse-S structure, which is not visible in soft X-ray, whilst in the quiet region filament, the curved southern half of the filament disappeared but the other half remained. Microwave observation provides information on the heated plasma propagating along the magnetic features. We examine thermal evolution within the sigmoidal filaments and compare the results with the tether-cutting scenario which was proposed for flare/filament eruptions. Possible magnetic reconnection that took place below the filament is discussed. | |
| Presentor: | Hugh Hudson |
| Title: | A rapidly-moving hard X-ray source and a CME |
| Authors: | Hudson, H. S. (SPRC)
Kosugi, T. (ISAS) Nitta, N. V. (LMSAL) Shimojo, M. (NoRH) |
| We have observed a high-speed coronal ejection in hard X-rays, detectable to an altitude of some 2~$\times$~10$^5$~km in the {\it Yohkoh} 33-53~keV energy bands. Simultaneous imaging at 17 and 34~GHz from the Nobeyama Radio Observatory shows complex moving features simultaneous with the ejection, including a compact source that we identify with the rapid X-ray source motion. The hard X-ray and microwave observations agree upon ejection velocities in the vicinity of 1000~km~s$^{-1}$. The hard X-ray sources also corresponded in position angle to a bright coronal mass ejection detected about 15 minutes later, and to both fast-drift and slow-drift radio bursts in the decimeter-meter bands. Other components of coronal hard X-ray emission were also detected, including an extended long-duration event with a hard spectrum. We suggest that a major eruptive flare occurred in NOAA region 9415, approximately 26$^\circ$ beyond the W limb at the time of the event. Estimating a source density of 4~$\times$~10$^9$~cm$^{-3}$ from the compact source observed at 17~GHz, we find a total electron number ($>$20~keV) of approximately N$_{20}$~$\sim$~2.5~$\times$~10$^{35}$ for the compact part of the source. | |
| Presentor: | Hiroaki Isobe |
| Title: | Statistical study of reconnection rate in solar falres |
| Authors: | Isobe, H (Kwasan and Hida Observatories, Kyoto University)
Morimoto, T (Kwasan and Hida Observatories, Kyoto University) Eto, S (Kwasan and Hida Observatories, Kyoto University) Narukage, N (Kwasan and Hida Observatories, Kyoto University) Shibata, K (Kwasan and Hida Observatories, Kyoto University) |
| The soft X-ray telescope (SXT) aboard Yohkoh has established that
the driving mechanism of solar flares is magnetic reconnection. However, the physics of reconnection has not been clarified. One of the current puzzles is: what determines the reconnection rateNULL The reconnection rate is defined as reconnected magnetic flux per unit time or equivalently the ratio of inflow speed into reconnection point to Alfven velocity in non-dimension, and is one of the most important physical quantities in reconnection physics. However, observations have not yet succeeded to statistically determine the reconnection rate because direct observation of reconnection inflow and coronal magnetic field is difficult. In this poster we present a method to determine the reconnection rate from observational data, which use the following relations: $H=(B^2 v_{in}L^2)/(4pi) v_{in}B=v_{foot}B_{foot}.$ Here $H,L,$ $v_{foot}$ and $B_{foot}$ are respectively the flare heating rate, size of the flare arcade, separation velocity of the two ribbon, and magnetic field strength of the foot points. Since these four quantities can be obtained from observational data, the relations above give the inflow velocity $v_{in}$ and coronal magnetic field $B$, and thus the reconnection rate can be determined. We have applied this method to 7 flares and 2 giant arcades and found that the reconnection rate $approx$ 0.001-0.1. | |
| Presentor: | Marian Karlicky |
| Title: | Drifting pulsations, 3 GHz oscillations and loop interactions in the June 6, 2000 flare |
| Authors: | Karlicky, M. (Astronomical Institute, 251 65 Ondrejov, Czech Republic)
Sawant, H.S. (Instituto Nacional de Pesquisas Espaciaias, INPE, C.P. 515, ) Fernandes, F.C.R. (Instituto Nacional de Pesquisas Espaciaias, INPE, C.P. 515, ) Cecatto, J.R. (Instituto Nacional de Pesquisas Espaciaias, INPE, C.P. 515, ) Farnik, F. (Astrnomical Institute, 251 65 Ondrejov, Czech Republic) Meszarosova, H. (Astronomical Institute, 251 65 Ondrejov, Czech Republic) Jiricka, K. (Astronomical Institute, 251 65 Ondrejov, Czech Republic) |
| During this long-lasting X2.3 flare (15:00-17:00 UT) two
3 GHz maxima (impulsive phases) were recognized at 15:06:46-15:07:00 and 16:26:34-16:26:42 UT. Quasi-periodic oscillations with the periods of 160 s and 11 s, respectively, were found, during both these impulsive phases. While in the first impulsive phase the 2.0-4.5 GHz broadband pulsations superimposed on the continuum were recorded, during the second one several quasi-periodic patches of narrowband spikes were observed in the frequency range of 2.5-3.5 GHz. Moreover, at the onsets of both impulsive phases the narrowband fast drift structures slowly drifting towards lower frequencies and indicating the plasmoid ejection were recorded. The SOHO and YOHKOH images of the flare show parallel loops with brightenings among them. It shows that the flaring loops interact. This view is supported by simultaneous observations of the quasi-periodic oscillations at 3 GHz and the narrowband pulsations in the second impulsive phase, which can be thus understood in the framework of the current loop coalescence model. | |
| Presentor: | Yukio Katsukawa |
| Title: | Small Fluctuation of Coronal X-Ray Intensity and a Signature of Nanoflares |
| Authors: | Katsukawa, Y (University of Tokyo)
Tsuneta, S (NAOJ) |
| If small energy events (nanoflares) contribute to the heating of the solar corona, they may be too small to be recognized as independent events. We analyze fluctuation of X-ray intensity observed with Soft X-Ray Telescope (SXT) aboard Yohkoh satellite to detect the tiny events which may occur in the solar corona. When we create a simple histogram of the X-Ray intensity fluctuation around mean intensity, we find that the histogram consists of a central Gaussian component and a wing component. The Gaussian component corresponds to random fluctuation around the mean X-ray intensity. The width of this component becomes broader with increasing intensity, and is larger than the width of the predicted photon noise distribution. We suggest that nanoflares produce the observed fluctuation of the X-ray intensity. We derive the analytical expression for the intensity fluctuation to estimate the individual energy of nanoflares from the observed intensity fluctuation. The intensity fluctuation can be related with the mean X-ray intensity, the energy of nanoflares, and the time scale of individual nanoflares. By comparing the observed fluctuation with the analytical expression, we are able to estimate the individual energy of nanoflares. The estimated energy ranges from $10^{20}$ to $10^{23}$ ergs. The observed fluctuation corresponds to an energy much smaller than previously predicted energy. It is estimated that if the energy of nanoflares is $10^{21}$ ergs, then these nanoflares must occur at a rate of $10^{5}$ s$^{-1}$ in a single active region ($\sim 10^{20}$ cm$^{2}$) to supply the required energy ($\sim 5 \times 10^7$ ergs cm$^{-2}$s$^{-1}$) to maintain the solar corona. | |
| Presentor: | Josef Khan |
| Title: | The solar coronal origin of a slowly drifting radio pulsation feature |
| Authors: | Khan, J. I. (Mullard Space Science Laboratory, UCL, U.K.)
Vilmer, N. (Observatoire de Paris, France) Saint-Hilaire, P. (Institute of Astronomy, ETH Zentrum & Paul Scherrer Institut) Benz, A. O. (Institute of Astronomy, ETH Zentrum, Switzerland) |
| We present an analysis of radio and soft X-ray imaging observations associated
with a slowly drifting decimetric-metric pulsation structure seen by the Phoenix-2 spectrometer at about 14:29 UT on 2000 August 25. This radio feature was closely associated with a solar flare. It has been suggested that such radio features may be associated with either chromospheric evaporation or plasmoid ejection during the flare impulsive phase. The range of frequencies over which this drifting radio feature occurred included frequencies observed by the Nanc{c}ay Radioheliograph enabling the spatial location and development of such a radio source to be determined for the first time. This flare was also observed by the {it Yohkoh/} Soft X-ray Telescope (SXT) allowing us to compare the radio locations with the development of coronal structures seen in soft X-rays. Our results indicate that the drifting pulsation feature for this event was closely associated with faint soft X-ray plasmoid ejection observed above the flare kernel region, not with the main chromospheric evaporation process. | |
| Presentor: | Diane Kisich |
| Title: | Scientist Involvement in High Visability Education and Public Outreach |
| Authors: | Kisich, D. (UC Berkeley, Space Sciences Laboratory)
Lewis, E. (NASA/Goddard Space Flight Center) |
| Our dynamic Sun offers exciting opportuni-ties to share research discoveries of NASAs Sun-Earth Connection with the pre-college education and public outreach communities. NASA's Sun-Earth Connection Education Fo-rum (SECEF), a partnership between UC Berkeley Space Sciences Laboratory and NASA/Goddard Space Flight Center, coordi-nates national programs for broad audiences that highlight solar and geospace missions and research programs. One of SECEFs primary goals is to facilitate scientist in-volvement in education and public outreach. We will show results of two high-visibility Solarevents - Sun-Earth Day and Eclipse 2001. These events involved more than 100 space scientists in schools, museums, and other venues across the nation, including members of minority professional societies, i.e. the National Society of Black Physicists. We will discuss lessons learned and future opportunities for scientist participation. (http://solarevents.org) | |
| Presentor: | Diane Kisich |
| Title: | Sharing the Sun-Earth Connection |
| Authors: | Kisich, D. (UC Berkeley, Space Sciences Laboratory)
Hawkins, I. (UC Berkeley, Space Sciences Laboratory) Vondrak, R. (NASA Goddard Space Flight Center) |
| Sharing the Sun-Earth Connection - the effects of our active Sun on geospace and beyond - is the primary goal of NASA's Sun-Earth Connection Education Forum (SECEF). SECEF is one of four national centers of space science education and public outreach funded by NASA's Office of Space Science. SECEF is a partnership between NASA/Goddard Space Flight Center and UC Berkeley Space Sciences Laboratory. We coordinate individual Education and Public Outreach (EPO) efforts from NASA Sun-Earth Connection missions and research programs, facilitating scientist involvement. SECEF develops products and sponsors programs in partnership with the pre-college and informal education communities that maximize the impact of individual efforts. We will show several examples of high-leverage products and programs for broad audiences that adapt and highlight Sun-Earth Connection data, research results, and scientist involvement. | |
| Presentor: | Bernhard Kliem |
| Title: | Correlated dynamics of hot and cool plasma in the main phase of a solar flare |
| Authors: | Kliem, B. (Astrophysical Institute Potsdam)
Dammasch, I. E. (MPAe, Katlenburg-Lindau) Curdt, W. (MPAe, Katlenburg-Lindau) Wilhelm, K. (MPAe, Katlenburg-Lindau) |
| We report far-ultraviolet observations of a solar limb flare obtained by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer. At a fixed pointing of the slit above the limb, spectra were simultaneously obtained in several emission lines that covered a wide temperature range from $approx!10^4$ to $approx!10^7$~K. The temporal
evolution of the spectra revealed a high degree of correlation between the dynamical behavior of hot ($Tsim10^7$~K) and cool ($Tsim10^4$~K) coronal material during the main phase of the flare. We note that the data did not show any indication of the presence of a prominence. Hot and cool plasmas brightened at nearly the same location. Their Doppler shifts, which were opposite to each other, reached peak values simultaneously. Thereafter the two components showed anti-correlated, rapidly damped, and oscillatory Doppler shifts and a very similar decay of the line widths, but with the cool plasma reaching maximum brightness before the hot plasma. This behavior points to an active role of cool plasma in the dynamics of this flare, different from the usual picture of passive cooling after the impulsive phase. We suggest a model in which localized cooling of coronal plasma by the thermal instability triggers magnetic reconnection through the resulting enhanced resistivity, the combined processes leading to the correlated dynamics of hot and cool plasma in a loop-loop interaction geometry. Results of a simulation confirming the triggering of reonnection by the thermal instability will be shown. We will also briefly present data of two partially similar events. | |
| Presentor: | James Klimchuk |
| Title: | Observation and Theory of Coronal Loop Structure |
| Authors: | Klimchuk, J. A. (Naval Research Lab)
Antiochos, S. K. (Naval Research Lab) Norton, D. (High Performance Fortran Associates) Watko, J. A. (Johns Hopkins University) |
| Following up on an initial study of 10 soft X-ray loops observed by {it Yohkoh} (Klimchuk et al. 1992), we have carefully examined 43 additional {it Yohkoh} loops and 24 EUV loops observed by {it TRACE}, and we confirm our original finding that most coronal loops have a nearly uniform thickness. This implies that: 1. the magnetic field in these loops expands with height much less than standard coronal models would predict; and 2. the shape of the loop cross section is approximately circular. We have investigated whether these surprising results can be explained by locally enhanced twist in the field, so that observed loops correspond to twisted coronal flux tubes. Our approach is to construct numerical models of fully three-dimensional force-free magnetic fields. To resolve the internal structure of an individual loop embedded within a much larger dipole configuration, we use a nonuniform numerical grid of size $609 \times 513 \times 593$, the largest ever applied to a solar problem, to our knowledge. Our models indicate that twist does indeed promote circular cross sections in the corona, even when the footpoint cross section is irregular. However, twist does not seem to be a likely explanation for the observed minimal expansion with height. | |
| Presentor: | Yuan-Kuen Ko |
| Title: | SOHO/UVCS And Yohkoh/SXT Observation of a High Temperature Corona Above an Active Region Complex |
| Authors: | Ko, Y.-K. (Harvard-Smithsonian Center for Astrophysics)
Raymond, J. C. (Harvard-Smithsonian Center for Astrophysics) Li, J. (Institute for Astronomy, University of Hawaii) Ciaravella, A. (Harvard-Smithsonian Center for Astrophysics) Michels, J. (Princeton Materials Institute, Princeton University) Fineschi, S. (Osservatorio Astronomico di Torino, Italy) Wu, R. (Harvard-Smithsonian Center for Astrophysics) |
| We present the results of the SOHO/UVCS and Yohkoh/SXT observation above an active region
complex (AR8194/8195/8198) at the southeast limb on April 6-7, 1998. This active region complex appears to be the base of a small streamer seen by LASCO/C2 at the southeast limb. UVCS was offset pointed to observe low in the corona from 1.22 R$_odot$ and up to 1.6 R$_odot$ with normal pointing. High temperature lines such as [Fe XVIII] $lambda 974$ and Ne IX $lambda 1248$ were present in this region implying that the electron temperature is higher than that in the quiet Sun corona. This region of the corona is also seen as particularly bright in Yohkoh/SXT, the SOHO/EIT high temperature filter (Fe XV $lambda 284$), and SOHO/LASCO C1. The electron temperature analysis indicates a two-temperature structure, one with $sim 1.5 imes 10^6$ K which is similar to that observed in the quiet Sun streamer, the other with a high temperature $sim 3.0 imes 10^6$ K. This two-temperature region likely corresponds to two distinct coronal regions overlapping in the line of sight. The electron temperature and emission measure profiles derived from the UVCS data are compared with those from the SXT data. The elemental abundances show a general FIP effect and decrease with height for all the elements. This is consistent with the effect of gravitational settling which, however, can not totally account for the observed elemental abundances. Other mechanisms that are likely to affect the coronal elemental abundance are discussed. | |
| Presentor: | Ken Kobayashi |
| Title: | Balloon-borne hard X-ray spectrometer for flare observation |
| Authors: | Kobayashi, K (University of Tokyo)
Tsuneta, S (National Astronomical Observatory) Tamura, T (National Astronomical Observatory) Kumagai, K (National Astronomical Observatory) Katsukawa, Y (University of Tokyo) Kubo, S (University of Tokyo) Sakamoto, Y (University of Tokyo) |
| We have developed a balloon-borne hard X-ray detector system for
observing high resolution hard X-ray spectra of solar flares. The first flight took place from Sanriku, Japan on August 29, 2001. While no flares occurred during the 3 hours of level flight, the instrument performed as expected. The instrument is designed to achieve a $3,mathrm{keV}$ energy resolution over the energy range of $15$--$100,mathrm{keV}$ in order to observe both non-thermal and thermal components of solar flare hard X-ray emissions. It uses an array of $16$ cadmium telluride detectors, each $10 imes 10 imes 0.5,mathrm{mm}$ in size. The instrument has no spatial resolution. We used CdTe detectors with Indium electrodes on one side which acts as a Schottky barrier to reduce leak current and improves energy resolution. Pre-flight tests indicated that all $16$ detectors achieved $3,mathrm{keV}$ resolution. The detectors are installed in a pressurized enclosure to prevent coronal discharge; the low-density ($0.1,mathrm{g},mathrm{cm}^{-2}$) CFRP/Rohacell window showed no leaks during testing or flight. The detectors are passively shielded by of $2,mathrm{mm}$ of lead, and field of view limited using a graded-Z (tungsten/tin/copper) collimator. To achieve optimal energy resolution these detectors need to be cooled to $0,^{circ}mathrm{C}$ or lower. Due to weight constraings this was achieved by using the detector enclosure surface as a radiator and maximizing radiative cooling. By placing shields around the detector to block sunlight and infrared radiation from the ground, and by optimizing the thermal properties of the radiator and shield surfaces, we achieved a stable temperature of $-13,^{circ}mathrm{C}$ at $41,mathrm{km}$ altitude. The detector pointing is fixed in the vertical direction, and azimuth is controlled with a motor placed above the gondola; the performance of the attitude control system was verified in flight. The instrument was recovered successfully after the flight and additional flights are being planned. | |
| Presentor: | Hiromichi Kozu |
| Title: | Convective Structure in Emerging Flux Region |
| Authors: | Kozu, H (Kwasan Observatory,Kyoto University,Japan)
Kitai, R (Kwasan Observatory,Kyoto University,Japanion) |
| The magnetic field in the Sun is created near the bottom of
convective layer and some of them emerges through convective zone as emerging flux loops. Flares, surges and other active phenomena can be triggered by the emerging flux which is affected by surrounding convective motion and convective structure can play an important role in basic mechanism of such active events. We observed emerging flux region NOAA 8582 in the G-band wavelength from 21:00UT to 23:30UT on 1999 June 11 with Real-time Frame Selector2 (RTFS2) installed in Domeless Solar Telescope in Hida Observatory, Kyoto University. We observed simultaneously H alpha center and its wing wavelength with Lyot filter system. We can see many emerging flux loops and surge activities during the observation period in H alpha data set. We applied Local Correlation Tracking Method (LCTM) to the G-band data set and derived horizontal convective structure in the upper convective zone from it. The resulting convective structure changed temporary and it can be interpreted as meso-scale convective structure. In addition to the varying convective structure we found a temporary continuous up-flow structure under emerging flux loops. The structure existed continually during the whole observation period and fixed to the position of middle of foot points of each flux loops. It means that the up-flow structure is characteristic of the emerging flux region. | |
| Presentor: | vinod krishan |
| Title: | Coronal loop modeling from frequency drift rate observations at decimetric wavelengths |
| Authors: | Krishan, V (Divisao de astrofisica)
Fernandes, F.C.R (same) Sawant, H.S. (same) |
| The frequency drift rates of the solar radio bursts are traditionally used todetermine the velocity of the exciting agency for a given coronal density model.Here, we derive the density model using the observed frequency drift rates of the decimetric bursts.It is also shown how the acceleration or the deceleration of the exciting agency(electron beam) of the decimetric emission can be inferred from the frequency drift rate and its time derivative.Attributing the deceleration to the collisional processes the coronal temperature can also be estimated.The deceleration time of the electron beam is also compared with its quasi linear relaxation time.The plasma parameters estimated from these decimetric observations suggest that the emission originates in coronal loops.These variations of the plasma parameters can be further confirmed by using high time and frequency resolution observations of the decimetric bursts. | |
| Presentor: | Mukul Kundu |
| Title: | Multiple-loop structure of a solar flare from Microwave, EUV and X-ray Imaging Data. |
| Authors: | Garaimov, V.I. (Astronomy department, University of Maryland, College Park,)
Kundu, M.R. (Astronomy department, University of Maryland, College Park,) |
| We present the results of analysis of a flare event of importance M2.8
that occured at 00:56 UT Aug 28, 1999. The analysis is based upon observations made with the Nobeyama Radio Heliograph(NoRH) and Polarimeters(NoRP), TRACE, SOHO/MDI,EIT and Yohkoh/SXT. MDI, TRACE, EIT, Soft X-ray and radio images show a very complex structure of the flaring region. Pre-flare TRACE and EIT images at 00:24UT show a small brightening in the region before the flare occured. The active region in which the flare occured had changing magnetic fields, and a new magnetic flux seems to have emerged. The X-Ray and radio time profiles for this event show a double peaked structure. The polarimeter data showed that the maximum radio emission (1200sfu) occured at 9.4 GHz. At 17GHz there appears to be four different radio sources including the main spot and the main flare loop. Most o fthe microwave emission seems to originate from the main flare loop. Comparison of BATSE and microwave time profiles at 17 and 34GHz from the main sunspot source shows that these profiles have similar structures and they coincide with the Hard X-ray peaks. The maximum of the flare loop emission was delayed by 10 sec relative to the second maximum of the sunspot associated flare emission. Analysis of SXT images during the post-flare phase shows a complex morphology - several intersecting loops and changes in the shape of the main flare loop. Implications of the complex morphology of both radio and X-ray flaring sources will be discussed. | |
| Presentor: | Mukul KUNDU |
| Title: | Possible Radio Evidence of Magnetic Reconnection in Solar Flares |
| Authors: | Kundu, M.R (University of Maryland,Coll.PK,MD,USA)
Grechnev, V.V (Inst.of Solar-Terr Phys.,Irkutsk,Ru) |
| We present possible radio evidence of magnetic reconnection in a solar flare- an LDE event of GOES class M3.2 that was observed on 1999 Feb16 on the disk.Our evidence is based
upon the facts that we observed a bright microwave source -blob at 17 and 34 GHz near the intersection of two apparently intersecting flaring loops or as a loop-top source above one flaring loop.The bright microwave source is clearly nonthermal and its time profile is similar to that of footpoint microwave sources; and in the late decay phase of the event the microwave source structure is similar to that of the corresponding SXR source. The flare was caused by a filament eruption that was observed in H-alpha by Hida Observatory.A shock( speed about 750 Km/s)must have been associated with the ejecta- which produced TypeII and IV bursts ( recorded by Hiraiso Observatory).There is evidence of disappearance of a filament during the event( TRACE 171 A images). | |
| Presentor: | Hiroki Kurokawa |
| Title: | PRE-FLARE HEATING AROUND THE TEMPERATURE MINIMUM REGION FOUND RIGHT PRIOR TO AN X-CLASS FLARE |
| Authors: | Kurokawa, H. (Kwasan and Hida Observatories, Kyoto University)
Wang, T. (Max-Plank Institute of Aeronomy) Ishii, T.T. (Kwasan and Hida Observatories, Kyoto University) Shine, R. (Lockheed Solar and Astrophysical Laboratory) |
| Studies of magnetic shear developments and pre-flare activities in flare-productive sunspot regions are fundamentally important for the study of flare energy build-up and energy release mechanism. Several previous works demonstrated that the emergence of a twisted magnetic flux rope ,which is originally formed in the convection zone, must be the source of the strong magnetic shear development in a sunspot region to produce a strong flare activity (Kurokawa 1987, Tanaka 1991, Ishii et al. 2000). We are still, however, far from sufficiently understanding how the twisted structures of a magnetic flux rope is formed in the convection zone, and where and how such a twisted magnetic rope untwists and releases its energy as flares? A flare productive active region NOAA 9026, which showed an interesting evolution during a coordinated observation between the Domeless Solar Telescope of Hida Observatory, Swedish Telescope of La Palma, and TRACE Satellite from 3 through 12 June of 2000, provided us a rare oppotunity to study a new important aspect of a twisted magnetic flux rope and its rapidly-untwisted motions to have caused strong flares. From the analyses of the evolution of this region, we first found a clear evidence of pre-flare heating or energy release from the upper photosphere through the lower chromosphere from about two hours before the energy release in the corona as an X-class flare. We suggest that this pre-flare energy release in the lower atmosphere is closely related to the emergence of the twisted magnetic flux rope from below the photosphere. | |
| Presentor: | Kanya Kusano |
| Title: | Magnetic Helicity Injection into the Solar Corona |
| Authors: | Kusano, K. (Hiroshima University)
Maeshiro, T. (Hiroshima University) Yokoyama, T. (NAOJ) Sakurai, T. (NAOJ) |
| We developed a new methodology to measure the magnetic
helicity injection into the solar corona based on the magnetograph observation, and studied the relationship between the helicity injection and the X-ray activity of active regions. The gauge-invariant helicity injection is given by $ dH/dt = int (vec{V}cdotvec{A}_p B_n + vec{A}_p cdot vec{B} V_n) dS, $ where $vec{V}$, $vec{B}$ and $vec{A}_p$ are the velocity, the magnetic field, and the vector potential for the potential field, respectively, and the subscript $_n$ denotes the normal component across the solar surface $S$. In order to calculate that from the magnetic data, first, the velocity tangential to $S$ is constructed by tracking the correlation among the sequential data observed by SOHO/MDI. Secondly, the normal velocity $V_n$ is calculated from the condition that the magnetic evolution $partial B_n/partial t$ must be consistent with the induction equation, $partial vec{B} / partial t = abla imes (vec{V} imes vec{B}).$ Since, for the latter process, not only the normal component but also the tangential component of the magnetic field is necessary, we use also the data observed by the vector magnetograph of Solar Flare Telescope in NAOJ, Tokyo. Through this procedure, the helicity injection in the active region NOAA 8100 is analyzed from 1997 Nov. 2 to 3. The results indicate that the injected helicity has a certain correlation with the X-ray activity of the active region. Furthermore, it is revealed that the helicity injected by the tangential velocity can supply sufficient free energy to be liberated in major flares. | |
| Presentor: | Barry LaBonte |
| Title: | Magnetic Fields in the Photosphere are not Force-free |
| Authors: | LaBonte, B.J. (Johns Hopkins University Applied Physics Laboratory) |
| Coronal magnetic fields are often inferred from the extrapolation of photospheric magnetic observations. The assumptions that the fields are potential or force-free are not correct in the photosphere. Therefore the extrapolation should be done by a method that accounts for this problem. | |
| Presentor: | Michelle Larson |
| Title: | Our Sun - the Star of Classroom Activities and Public Outreach Events |
| Authors: | Craig, N. (UC Berkeley)
Larson, M. B. (UC Berkeley) |
| We will present innovative classroom activities for grades 8-12, as well as public outreach web-based resources featuring solar data, mathematics, and solar scientist interviews. These resources have been developed through partnerships between NASA scientists and educators. The classroom activities are well-aligned with National Science Education Standards. | |
| Presentor: | Michelle Larson |
| Title: | The Yohkoh Public Outreach Project |
| Authors: | Larson, M. (UC Berkeley)
Acton, L. (Montana State University) McKenzie, D. (Montana State University) Slater, T. (University of Arizona) Alexander, D. (LMSAL) Freeland, S. (LMSAL) Lemen, J. (LMSAL) |
| The NASA funded Yohkoh Public Outreach Project (YPOP) began in 1995 with the goal of providing public access to high quality Yohkoh SXT data via the World Wide Web. The project utilizes the intrinsic excitement of the SXT data, and in particular the SXT movies, to develop science learning tools and classroom activities. The WWW site at URL: http://www.lmsal.com/YPOP/ uses a movie theater theme to highlight available Yohkoh movies in a format that is entertaining and inviting to non-scientists and well received by scientists. We will discuss the wide range of people YPOP has reached over the past six years, as well as lessons learned during the development of the project. | |
| Presentor: | Youping Li |
| Title: | On Broadening Mechanism of CaXIX Resonance Line in Solar Flares |
| Authors: | Li, Y.P. (Purple Mountain Observatory)
Gan, W.Q. (Purple Mountain Observatory) |
| On Broadening Mechanism of CaXIX Resonance Line in Solar Flares
Y.P. LI and W. Q. Gan Purple Mountain Observatory, Nanjing 210008,China There are two explanations for the broadening mechanisms of the CaXIX resonance line at the rising phase of a solar flare. One is due to the velocity dispersion of the chromospheric evaporation along the loop; the other is due to the nonthermal turbulence resulted from the flare energy releasing. In this poster we distinguish these two possibilities by studying the influence of the loop orientation on the broadening of the CaXIX resonance line, based on the data observed with SXT and BCS on Yohkoh. The results seem to support that the broadening of the CaXIX resonance line is caused by the nonthermal turbulence, rather than by the velocity dispersion. | |
| Presentor: | Jing Li |
| Title: | The Nature of Large-scale and Long-lived Coronal Structures |
| Authors: | Li, J. (University of Hawaii)
LaBonte, B. (University of Hawaii) Acton, L. (Montana State University) Slater, G. (LMSAL) |
| The presentation will summarize our recent work on the large-scale, long-lived coronal streamers based on limb synoptic maps made from Yohkoh/SXT and SOHO/EIT images. The number of properties of such coronal streamers have been revealed on the limb synoptic maps: 1. They originate from active regions and have large extent in both latitude and altitude. 2. Because they are large in 3-dimension, they largely control the visibility of polar hole regions. When the active region is in close side of the sun, then may cover the polar holes. When the active region is at far side of the sun, they can be seen above the solar limb by projections; 3. The life time of such large-scaled coronal streamers can be up to 10 solar rotations; 4. These structures are associated with underlying, non-contemporaneous spot clusters; 5. Individual spots in the clusters are short-lived, but contribute magnetic flux collectively to form the long-lived coronal features. | |
| Presentor: | Yuri Litvinenko |
| Title: | A simple estimate for energies of electrons accelerated in flare current sheets on the Sun |
| Authors: | Litvinenko, Y. E. (University of NH) |
| A major result from Yohkoh is the frequency of hard X-ray sources above
the flare loops. Observations suggest that electron acceleration in flares occurs in the magnetic reconnection region above the loop. Unfortunately, models for particle acceleration in reconnecting current sheets predict electron energy gains in terms of the reconnection electric field and the thickness of the sheet, both of which are extremely difficult to measure. It can be shown, however, that application of Ohm's law in a turbulent current sheet, combined with energy and Maxwell's equations, leads to a formula for the electron energy gain in terms of the flare power output, the magnetic field strength, the plasma density and temperature in the sheet and its area. Typical flare parameters correspond to electron energies between a few tens of keV and a few MeV. | |
| Presentor: | Maria Madjarska |
| Title: | Dynamics and diagnostics of explosive events and blinkers |
| Authors: | Madjarska, M.S. (Armagh Observatory, Armagh, BT61 9DG, N. Ireland)
Doyle, J.G. (Armagh Observatory, Armagh, BT61 9DG, N. Ireland) Teriaca, L. (Osservatorio Astrofisico di Atcetri, 50125 Firenze, Italy) |
| The knowledge of the main physical parameters of UV explosive events and blinkers, such as density and temperature, is of great importance for
the better understanding of the true nature of these transient events. In this context, density and temperature diagnostics based on lines belonging to O~{sc iv} 1400 AA and O {sc iii} multiplets is presented for both kind of events.The dynamics of the solar transient phenomena is revealed through their temporal and spatial evolution as observed in spectral lines covering a wide temperature range. The results are obtained using SUMER, CDS, MDI and EIT aboard SoHO, TRACE and Big Bear Solar Observatory observations and are aimed to give more information about the main properties of these phenomena. The events are also studied in connection with the evolution of the underlying magnetic field, searching for observational evidences of their further propagation higher in the solar corona. | |
| Presentor: | Tetsuya Magara |
| Title: | Sigmoid Structure of an Emeging Flux Tube |
| Authors: | Magara, T. M. (Montana State University)
Longcope, D. W. L. (Montana State University) |
| We present the results from three-dimensional magnetohydrodynamic (MHD) simulations of a magnetic flux tube emerging through the solar photosphere. The simulation is initialized with a straight tube of twisted magnetic field located in the upper convection zone. Buoyancy effects drive an arched segment of the tube upward through the photospheric layer and into the corona. Matter drains from the coronal field which thereafter undergoes a rapid expansion. The coronal magnetic field formed in this manner exhibits outer poloidal field lines resembling a potential arcade, and inner toroidal field lines, which emerge after the tube axis, forming sigmoid structure. The simulations suggest that neutral-line shear and sigmoidal field arise as a natural by-product of flux emergence. | |
| Presentor: | Petrus Martens |
| Title: | The Origin of Prominences and Their Hemispheric Preferences for Chirality and the Skew of Overlying X-ray Loops |
| Authors: | Martens, P.C. (MSU) |
| I present a ``head-to-tail'' linkage model for the formation, evolution, and eruption of solar filaments. The magnetic field structure of the model is based upon the observation that filaments form exclusively in filament channels with no apparent magnetic connections above the polarity inversion line. The formation of a filament in this configuration is driven by flux convergence and cancellation, which produces loop-like filaments segments with a half-turn. Filament segments of like chirality may connect and form long quiescent filaments. I demonstrate that the combined workings of Hale's polarity law, Joy's law, and differential rotation introduce a strong hemispheric preference in the chirality of filaments formed poleward of the sunspot belt, in agreement with observations. I analyze the magnetic fine structure of filaments formed through the model and find consistency with the observed hemispheric preference for the skew of overlying X-ray emitting loops observed by Yohkoh-SXT, contrary to what would be expected from differential rotation. Finally I show that every cancellation event that generates a filament obeying the hemispheric chirality preference, injects a flux tube below the surface with a poloidal field opposite to that of the ongoing cycle. I suggest that this pattern of submergence of flux represents the specific mechanism for the reversal of the poloidal flux in a Babcock-Leighton-Durney type model for the solar dynamo. | |
| Presentor: | Helen Mason |
| Title: | Active Region Studies with SOHO-CDS |
| Authors: | Mason, H.E. (Univ of Cambridge)
Del Zanna, G. (Univ of Cambridge) |
| Spectral observations with SOHO-CDS provide an opportunity
to study the development of active region structures. In particular, it is possible to determine the plasma properties: temperature and electron density distribution, elemental abundances and mass motions. The nature of enhancements in the transition region emission is investigated. | |
| Presentor: | Satoshi Masuda |
| Title: | Hard X-ray Solar Flares Revealed with Yohkoh HXT -- A Review |
| Authors: | Masuda, S. (STEL, Nagoya University) |
| Yohkoh/HXT has detected more than 2500 solar flares over its 10 years of operation. Compared with earlier hard X-ray imagers, HXT has several advantages, such as a larger effective area ($\sim$ 60 cm$^2$), a wider energy range (14 -- 93 keV) divided into four energy channels, a higher spatial resolution ($\sim$ 5 arcsec), and a higher time resolution (0.5 sec). In the first five years of operation, HXT provided us with a lot of new information on solar flares. Some of its major achievements are as follows: \begin{itemize} \item Providing both statistical and detailed event studies of double footpoint sources \item Discovery of the above-the-looptop source as evidence for magnetic reconnection \item Revealing characteristics of a super-hot ($> 30$ MK) thermal component \end{itemize} These new results clearly indicate that many types of hard X-ray sources simultaneously exist even in a single flare. For this reason, the imaging-spectroscopy technique becomes very important for investigation of an individual source in the hard X-ray energy range. There is no doubt that collaborative research using SXT made these HXT results more meaningful. Of course, the use of other correlative data is also important. For example, data from CGRO gave us information on the electron acceleration site, and information provided by the Nobeyama radio heliograph showed a three-leg structure of solar flares and streaming electrons in that structure. After the current solar cycle started, HXT has detected many intense flares. Recently several characteristics of these flares have been identified. Some of these are: \begin{itemize} \item Motion of hard X-ray footpoint sources with a high temporal resolution in the 06-Nov-1997 event \item High-altitude diffuse hard X-ray source with a hard spectrum in the 23-Apr-1998 event \item Detailed analysis of the above-the-looptop source in the 18-Aug-1998 events \item Two-ribbon structure in the 14-Jul-2000 event \item Moving coronal hard X-ray source in the 18-Apr-2001 event \end{itemize} \indent These observational results and interpretations are summarized in this paper. | |
| Presentor: | Sarah Matthews |
| Title: | Multi-wavelength observations of Yohkoh white-light flares |
| Authors: | Matthews, S.A. (Mullard Space Science Lab., University College London)
van Driel-Gesztelyi, L. (Observatoire de Paris; Mullard Space Science Lab., Universit) Nitta, N. (Lockheed Martin Solar and Astrophysics Lab.) Hudson, H.S. (SPRC/ISAS) |
| The problem of accounting for the continuum emission that
is observed in solar flares is still one which is largely unresolved. These white-light flares place severe constraints on the energy requirements and transport mechanisms operating in the flare, raising the question of whether partial or total in-situ heating is required to account for this deep atmospheric heating. Since it is widely believed that the energy release in solar flares occurs in the corona and that energy is then transported to the low chromosphere where the optical emission is produced, most attempts to explain the origin of white-light flares have centred on canonical mechanisms. However, it has become clear that the spatial and temporal correspondence between white-light and HXR is not one-to one. In order to further our understanding of these events we study the temporal and spatial relationships between emission in the visible, SXR and HXR regimes in all of the white-light flares observed by Yohkoh prior to the failure of the Soft X-ray Telescope (SXT) Aspect Camera in 1992; a total of approximately 30 events. | |
| Presentor: | Alan McAllister |
| Title: | The Skew of Polar Crown X-ray Arcades Over The Solar Cycle |
| Authors: | McAllister, A.H. (Helio Research)
MacKay, D.H. (St. Andrews University) Martin, S.F. (Helio Research) |
| Historical measurements of the axial fields of polar crown
filaments [Rust, LeRoy], have produced an ordered and consistent picture, with uniform direction on each polar crown, opposite in the two hemispheres, and reversing along with the polar reversals at the peak of each solar cycle. This pattern was extended by Martin, Bilimoria, and Tracadas to four solar cycles, based on topological filament techniques coupled with photospheric magnetic field measurements. The pattern based on this work is inconsistent with the expected effects of differential rotation on east-west filament channels, and has led to various theories of filament formation that specifically address these observations. Martin and McAllister found a one-to-one relationship between the chirality of filament channels and the skew (relative orientation) of the overlying coronal arcades, as seen with the Yohkoh Soft X-ray Telescope (SXT). This result was based on mid-latitude observations. Coupling these two results predicts the skew of polar crown arcades in solar cycles 22 and 23. A survey of the SXT images over the whole declining phase of cycle 22 (Oct. 1991 to June 1995) produced results opposite to what had been expected, polar crown arcades that were opposite the dominant hemispheric pattern and oriented in a direction consistent with differential rotation [McAllister and MacKay]. However, the SXT results are in agreement with efforts by MacKay and Van Ballegooijen to simulate global filament formation patterns. The absence of simultaneous measurements of filament and arcade topologies and fields leaves us with several observational pieces that do not readily fit together. In this paper we will review this puzzle and present new results from a preliminary survey of polar arcades in the rising phase of cycle 23. These will be compared with previous results and with the MacKay and Van Ballegooijen simulations for the rise phase of the solar cycle. | |
| Presentor: | Mark McConnell |
| Title: | Prospects for Hard X-Ray Solar Flare Polarimetry with HESSI |
| Authors: | McConnell, M.L. (University of New Hampshire)
Smith, D.M. (University of California - Berkeley) Emslie, A.G. (University of Alabama - Huntsville) Lin, R. (University of California - Berkeley) Ryan, J.M. (University of New Hampshire) |
| Although designed primarily as a hard X-ray imager and spectrometer, the High Energy Solar Spectroscopic Imager (HESSI) is also capable of measuring the polarization of hard X-rays (30-100 keV) from solar flares. This capability arises from the inclusion of a small unobstructed Be scattering element that is strategically located within the cryostat that houses the array of nine Germanium detectors. The Germanium detectors are segmented, with both a front and rear active volume. Low energy photons (below about 100 keV) can reach a rear segment of a Ge detector only indirectly, by scattering. Low energy photons from the Sun have a direct path to the Be and have a high probability of Compton scattering into a rear segment of a Ge detector. The azimuthal distribution of these scattered photons carries with it a signature of the linear polarization of the incident flux. Prelimary estimates suggested that a 30-100 keV polarization sensitivity of less than a few percent could be achieved for X-class flares. We shall describe this detection process in detail and present the latest results from detailed simulations of the polarimetric capability of HESSI. We will also review some of the practical issues with regards to the analysis of HESSI data that may be important for polarization studies. | |
| Presentor: | David McKenzie |
| Title: | Signatures of Reconnection in Eruptive Flares |
| Authors: | McKenzie, D. E. (Montana State University) |
| Solar flares are defined by magnetism. The energy that is stored up, transferred, and released is done so in and by the magnetic fields of the Sun; the structures in which the flares occur are wholly dependent on the configuration of magnetic connections; and it is the rearrangement of these connections that we believe plays such a large and important role in many of the processes observed in flares. Many of our theoretical pictures of flare mechanisms rely in some part on magnetic reconnection, and one by one the observable signatures of these models are being uncovered in chromospheric and coronal data. These data, in turn, introduce observational constraints that help to drive the models. I will summarize some key observations that have helped to support the case for reconnection, and that have helped us to peer more deeply into the behavior of coronal plasmas and magnetic fields. | |
| Presentor: | Rebecca McMullen |
| Title: | Modeling the Transient Brightening of an X-ray Bright Point Coronal Loop |
| Authors: | McMullen, R. A. (Montana State University)
Longcope, D. W. (Montana State University) Kankelborg, C. C. (Montana State University) |
| We study the spatial structure and temporal evolution of an X-ray bright point loop in order to understand the role of magnetic energy dissipation. We use a time-dependent gasdynamic model to simulate the corona and transition region in the x-ray bright point's coronal loop. For this work we model a bright point observed by TRACE and SOHO on June 17, 1998, where the magnetic field geometry is derived from an extrapolation of magnetograms. We study the effects of various spatial and temporal distributions of heat deposition within the loop. The quantity of energy deposited and the location of the energy release is constrained by a model equilibrium magnetic field. We model the observed transient brightening of the bright point as a series of nanoflare events.
| |
| Presentor: | Thomas Metcalf |
| Title: | The Magnetic Free Energy in Active Region 8299 |
| Authors: | Metcalf, T. R. (Lockheed Martin Solar and Astrophysics Laboratory)
Mickey, D. L. (University of Hawaii, Institute for Astronomy) LaBonte, B. J. (University of Hawaii, Institute for Astronomy) Ryder, L. A. (Lockheed Martin Advanced Technology Center) |
| We calculate the magnetic free energy as a function of time for NOAA active
region 8299 on 1998 August 11 using vector magnetic field measurements in the ion{Na}{1} 5896AA sepctral line observed with the Imaging Vector Magnetograph at Mees Solar Observatory. The free energy in this active region is significant with a magnitude of about $10^{33}$ ergs, though the active region was not flare productive. This amount of free energy is more than enough to explain the enhanced heating of the active region corona. The free energy dipped to a value consistent with zero for one hour during the observation. {it Yohkoh}/SXT images reveal that during this dip in the free energy, the coronal structure of AR 8299 and the nearby AR8297 changed significantly. SXT observed the brightening of a coronal loop connecting AR 8299 and AR 8297 and observed coronal dimming and the formation of a cusp structure in AR 8297, suggesting that a gradual CME was launched as the magnetic energy dipped. Unfortunately, LASCO data were not available to confirm the existence of a halo CME. However, the circumstantial evidence points to the magnetic free energy as the energy source for the postulated CME. | |
| Presentor: | James Miller |
| Title: | Solar Energetic Particle Spectra from Impulsive Flares |
| Authors: | Miller, J A (Univ of Alabama in Huntsville)
Mason, G M (Univ of Maryland) |
| Impuslive solar flares present a wealth of diagnostic information pertaining to their acceleration mechanism, ranging from radio and microwave emission, to soft and hard X-rays, and to gamma-ray line and continuum emission. However, perhaps the most important from a particle acceleration perspective are the solar energetic particles (SEPs) observed in interplanetary space. It has long been known that these particles have peculiar, and in some instances spectacular, abundance enhancements. For instance, the He-3 to He-4 ratio is enhanced by a factor of 2000 over the ambient coronal value, and Fe, Ne, Mg, and Si suffer smaller but still significant enhancements over C, N, O. These enhancements provide valuable insight into the nature of particle acceleration in impulsive events. Recently, instruments (ULEIS and SIS) on the Advanced Composition Explorer (ACE) have yielded ion spectra over broad energy ranges, which further enhance the diagnostic capability of SEPs.
In this paper, we consider further a model for particle acceleration in impulsive solar flares that employs cascading MHD turbulence. It has already been shown that low-amplitude MHD turbulence, assumed to be generated during the energy release, cascades from low to high frequencies and leads to heavy ion acceleration with energy-integrated abundances that are in agreement with observations. We will now present the heavy ion distributions and demonstrate how they self-consistently fit the distributions observed by ACE. Such fits provide further evidence of the validity of this model for impulsive flare acceleration. | |
| Presentor: | Takehiro Miyagoshi |
| Title: | Three dimensional MHD Numerical Simulations for a Magnetic Twisted Emerging Flux Tube |
| Authors: | Miyagoshi, T.M (National Astronomical Observatory, Japan)
Yokoyama, T.Y (National Astronomical Observatory, Japan) |
| It is well known that an emerging flux tube causes various active
phenomena in the solar atmosphere. They are, for example, an active region formation, flares, CMEs, and so on. For this reason, understanding the evolution of an emerging flux tube is very important. Twisted flux tube is important because it contains substantial magnetic energy, and is thought to be a source of violent phenomena. We have studied behaviors of a twisted emerging flux tube from the upper convection zone to the corona by means of three-dimensional MHD numerical simulations because of twist of tubes, three dimensional morphology for argument. Initially, a Gold-Hoyle force-free flux tube is set in the upper convection zone, and started emerging by Parker instability with imposed small amplitude perturbation. We aimed to solve evolution of flux tubes in the upper solar atmosphere and formation of magnetic structure in the corona. Important parameters are magnitude of twists, radius of a flux tube, and wavelength of perturbation. The results of our simulations show that an S-shaped structure is formed when magnitude of twists is strong ($B_{ heta} = frac{qrB_0}{1+(qr)^2}, qsim 1.0 $), and a filament structure is formed when magnitude of twists is weak ($qsim 0.2$). Other parameter dependence is discussed in our paper. | |
| Presentor: | Ronald Moore |
| Title: | Contagious Coronal Heating from Recurring Emergence of Magnetic Flux |
| Authors: | Moore, R. L. (MSFC/NSSTC)
Falconer, D. A. (MSFC/NSSTC/UAH) Sterling, A. C. (MSFC/NSSTC/UAT) |
| For each of four old bipolar active regions, we present and interpret Yohkoh/SXT and SOHO/MDI observations of the development, over several days, of enhanced coronal heating in and around the old bipole in response to new magnetic flux emergence within the old bipole. The observations show:
1. In each active region, new flux emerges in the equatorward end of the old bipole, around a lone remaining leading sunspot and/or on the equatorward end of the neutral line of the old bipole. 2. The emerging field is marked by intense internal coronal heating, and enhanced coronal heating occurs in extended loops stemming from the emergence site. 3. A rooster tail of coronal loops in the poleward extent of the old bipole undergoes brightenings and becomes more extensive in response to the flux emergence. 4. There are episodes of enhanced coronal heating in surrounding magnetic fields that are contiguous with the old bipole but are not directly connected to the emerging field. From these observations, we suggest that the accommodation of localized newly emerged flux within an old active region entails far reaching adjustments in the 3D magnetic field throughout the active region and in surrounding fields in which the active region is embedded, and that these adjustments produce the extensive enhanced coronal heating. We also note that the reason for the recurrence of flux emergence in old active regions may be that active-region flux tends to emerge in giant-cell convection downflows. If so, the poleward rooster tail is a coronal flag of a long-lasting downflow in the convection zone. This work was funded by NASAs Office of Space Science through the Solar Physics Supporting Research and Technology Program and the Sun-Earth Connection Guest Investigator Program. | |
| Presentor: | Taro Morimoto |
| Title: | Determination On Eruptive Or Quasi-Eruptive Of Solar Disappearing Filaments And Their Accelerations |
| Authors: | Morimoto, T (Hida and Kwasan Observatories, Kyoto University)
Kurokawa, H (Hida and Kwasan Observatories, Kyoto University) |
Many observations at the solar limb showed that CMEs are often associated with eruptions of H$\alpha$ prominences. Those CMEs, when directed to the earth, are known to cause geomagnetic storms. The observation of disappearace of H$\alpha$ filaments is, therefore, important not only to study the drive mechanisms of CMEs but also to forecast the geomagnetic storms. However, it is usually difficult to know whether a disappearing filament is eruptive or not, because the ordinary patrol observations in only H$\alpha$ line center cannot provide enough information of velocities in the disappearing filament. Using the Flare Monitoring Telescope at Hida Observatory which can observe simultaneously in both H$\alpha$ line center and line wings, we analyzed events H$alpha$ solar filament disappearance. This study is new in the following points. \begin{enumerate} \item We classified these events into "eruptive" or "quasi-eruptive" by deriving 3-D velocity field of H$\alpha$ disappearing filaments. \item We examined the coronal responses, such as flares and coronal arcade formations, which were associated with H$\alpha$ events, using \textit{Yohkoh}/SXT data. \item We analyzed a large number of samples (34). \end{enumerate} The 3-D velocity fields were determined from measurement of apparent and line of sight velocity of filaments. Our method of getting line of sight velocity is based on Beckers' cloud model (Beckers 1966). With these obsevations and anlyses described above, we obtained the following results. 1) All H$\alpha$ events were followed by significant changes in coronal strucutre. 2) Making use of temperature and emission measure analysis of \textit{Yohkoh}/SXT data, we found that thermal energy release rate in enhanced coronal plasmas is greater in active region than in quiet region. 3) The observed time scales of filament accelerations are directly related to the Alfven transit time scales computed with magnetograms. | |
| Presentor: | Satoshi Morita |
| Title: | 3-D Structure of Arcade Type Flares Deduced from Soft X-ray Observations of a Homologous Flare Series |
| Authors: | Morita, S (Science University of Tokyo)
Uchida, Y (Science University of Tokyo) Hirose, S (Science University of Tokyo) |
| In the solar flare problems, no ultimate model that matches observations has been established. One of the reasons for this is due to the restrictions in the observational data lacking information about the third dimension. Thus, many researchers have tried to get information about the three dimensional (3-D) coronal structures by using various techniques or ideas; like movie analysis, calculations using vector or line-of-sight components of photospheric magnetic data, and etc.. In the near future, a mission named STEREO which will obtain information about the 3-D coronal structures from two satellites, is planned. In the present paper, we noted the homology in a homologous flare series of February 1992. We derived a 3-D coronal structures by making use of the images obtained from the three different sight-lines at some common phases in them with Yohkoh SXT. The result of this analysis has made it clear that the so-called ``cusped arcade'' at the maximum phase in the well-known 1992 February 21 flare is, contrary to the general views, an ``elongated arch'' seen with a shallow oblique angle. It is not the ``flare arcade'' seen axis-on as widely conceived. This elongated arch coincides roughly with a diagonal of the main body of the "soft X-ray arcade" that came up later. The magnetic structure causing the flare as a whole turned out in this analysis to be a structure with quadruple magnetic sources. The relative locations of these four characteristic sources stayed almost the same throughout the period of this homologous flare series, determining the fundamental shape of this homologous series. We also examined the corresponding features for other similar events, also using information from other satellites, and will report the results. | |
| Presentor: | Shin'ichi Nagata |
| Title: | Multi-temperature structure of the solar corona observed by Yohkoh and SoHO |
| Authors: | Shin'ichi Nagata, SN (Institute of Space and Astronautial Science) |
| A suite of XUV Doppler Telescope (XDT), {it Yohkoh} Soft X-ray
Telescope (SXT) and SOHO Extreme-ultraviolet Imaging Telescope (EIT) images allow us to see whole temperature evolution of coronal loops. We show that hot loops seen in SXT images ($T>3$ MK) and cool loops seen in EIT/XDT images ($T=$ 1--2 MK) sometimes exist in spatially alternate way. We follow the time evolution of several hot (SXT) and cool (EIT 195 {AA}) loops and found that their anti-coincidence is conserved for much longer than their estimated cooling time scales. This suggests that each loop has its own destined heating rate, and that there are high heating-rate loops and low heating-rate (dormant) loops. | |
| Presentor: | Tomoko Nakagawa |
| Title: | NOZOMI observation of interplanetary transients ejected as limb CMEs |
| Authors: | Nakagawa, T (Tohoku Institute of Technology)
Matsuoka, A (Institute of Space and Astronautical Science) NOZOMI/MGF team, NONE (NONE) |
| The interplanetary magnetic field data obtained by
NOZOMI spacecraft were used for the study of interplanetary objects which were ejected as CMEs from the limb of the Sun. The Nozomi spacecraft, launched in 1998 as a Japanese Mars Explorer, spends more than 5 years in interplanetary space until its insertion into Martian orbit. Some of the scientific instruments including the magnetometer is operating in its trans-Mars orbit. Nozomi was located at a radial distance of 1.38 AU from the Sun and 83$^o$ -- 97$^o$ to the east from the Earth's position during the period from November 1, to November 30, 1999. The large separation from the Earth in heliospheric longitude enabled direct detection of the ejecta launched into interplanetary space in a direction perpendicular to the line of sight of the imagers such as Yohkoh and SOHO. Non-stational magnetic structures were detected by comparing Nozomi observation with that of ACE spacecraft located near the Earth. Among them, non-stational structures with non-spiral magnetic field were detected as interplanetary transients. On their launch time calculated from the solar wind speed, CMEs were found on the east limb of the Sun. Some of them had initial speeds consistent with those of interplanetary observation, but others did not. The interplanetary magnetic field structures showed wide range of variations from event to event. | |
| Presentor: | Noriyuki Narukage |
| Title: | Simultaneous observation of a Moreton wave on Nov 3, 1997 in H-alpha and Soft X-ray |
| Authors: | Narukage, N (Kwasan and Hida Observatories, Kyoto Univ.)
Shibata, K (Kwasan and Hida Observatories, Kyoto Univ.) Hudson, H (SPRC) Eto, S (Kyoto Univ.) Isobe, H (Kwasan and Hida Observatories, Kyoto Univ.) Asai, A (Kwasan and Hida Observatories, Kyoto Univ.) Morimoto, T (Kwasan and Hida Observatories, Kyoto Univ.) |
| Moreton waves are flare-associated waves observed to propagate across the solar disk in H-alpha (Moreton, 1960). Such waves have been identified as the intersections of a coronal fast-mode shock fronts and the chromosphere (Uchida, 1967). We report the observation of a Moreton wave in H-alpha (line center and +/- 0.8 A) with the Flare Monitoring Telescope (FMT) at the Hida Observatory of Kyoto University at 4:37-4:41 UT on November 3, 1997. The same region (NOAA 8100) was simultaneously observed in soft X-rays with the Soft X-ray Telescope (SXT) on board Yohkoh, and a wave-like disturbance ("X-ray wave") was also found. The position of the wave front as well as the direction of propagation of the X-ray wave roughly agree with those of the Moreton wave, though the exact positions of the two waves differ perceptibly. The propagation speeds of the Moreton wave and the X-ray wave are about 450 km/s and 600 km/s, respectively. Assuming that the X-ray wave is the MHD fast shock, we can estimate the propagation speed of the shock, based on the MHD shock theory and the observed soft X-ray intensities ahead and behind the X-ray wave front. It is found that the estimated fast shock speed is 550-800 km/s, in rough agreement with the observed propagation speed of the X-ray wave. The fast mode Mach number of the X-ray wave is also estimated to be about 1.6. These results suggest that the X-ray wave is a MHD fast shock propagating through the corona and hence is the coronal counterpart of the Moreton wave. | |
| Presentor: | Richard Nightingale |
| Title: | Concurrent Rotating Sunspots, Twisted Coronal Fans, Sigmoid Structures, and Coronal Mass Ejections |
| Authors: | Nightingale, R W (Lockheed Martin Solar & Astrophysics Laboratory)
Shine, R A (Lockheed Martin Solar & Astrophysics Laboratory) Brown, D S (University of St. Andrews and LMSAL) Wolfson, C J (Lockheed Martin Solar & Astrophysics Laboratory) Schrijver, K J (Lockheed Martin Solar & Astrophysics Laboratory) Metcalf, T R (Lockheed Martin Solar & Astrophysics Laboratory) Title, A M (Lockheed Martin Solar & Astrophysics Laboratory) |
| In an on-going study, several sunspots, in apparent rotation, have been identified in TRACE photospheric white light (WL) images with accompanying twisting of coronal fans in the corresponding EUV (171, 195 $AA$) images. These observations can also be temporally and spatially associated with S or inverse-S shaped regions (sigmoid structures) appearing in Yohkoh SXT images and with concurrent coronal mass ejections (CMEs) and/or flares. We have determined the rotational speed of the apparently rotating sunspot in AR 9114 over 8-10 August 2000, established the inverse S shape observed in the SXT data, and viewed a rapid, bright flash of possible reconnection in a TRACE EUV movie. A CME was observed during the 15-18 August 1999 event, which also included an inverse S shaped region in the SXT data, and a rotating sunspot and twisting coronal fans in the TRACE data. The large Bastille Day CME event of 14 July 2000 was accompanied by one or more apparently rotating sunspots as observed in TRACE WL and by an inverse S shaped region as seen in a difference SXT image. Movies and plots of some of these data will be shown along with flow maps and a list of the pertinent parameters for several rotating sunspots. We will report on our attempt to determine the vertical electric current flowing through the 8 August 2000 sunspot utilizing the Mees vector magnetograph data in order to better understand the apparent rotation "driver". These observations display the coupling of the solar magnetic field from the photosphere into the corona. | |
| Presentor: | Nariaki Nitta |
| Title: | On the Relation between Flares and CMEs |
| Authors: | Nitta, N. V. (LMSAL)
Hudson, H. S. (SPRC/UCB/UCSD) |
| It is now widely accepted that severe geomagnetic storms and
intense solar energetic particle (SEP) events are due to coronal mass ejections (CMEs) and CME-driven shocks. However, a large fraction of fast and extended CMEs are associated flares, and the relation of CMEs with flares is still an unsettled issue. We point out that different types of flares exist that are associated with CMEs. Based on our finding that energetic CMEs could not only be associated with long decay events (LDEs) but also with impulsive flares, we propose that a given event is a mixture of the CME and flare processes. Both of them may involve mass ejection and heating/acceleration, but in different ways. The magnetic field may critically affect which process is more effective in each event. We discuss this view in terms of the more physics-based (but less observation-based) concept that CMEs and flares represent the release of magnetic helicity and energy, respectively. As a related topic, the relation between coronal and interplanetary shocks is revisited on the basis of new data analysis. | |
| Presentor: | Masamitsu Ohyama |
| Title: | Timing and Occurrence Rate of X-Ray Plasma Ejections |
| Authors: | Ohyama, M. (Shiga University)
Shibata, K. (Kwasan and Hida Observatories, Kyoto University) |
| We examined 126 limb flares between October 1991 and August 1998. X-ray plasma ejections are found in 54 flares.
All X-ray plasmoids are detected in images taken before the maximum peak of hard X-ray (HXR) emission or in each first image after the HXR peak. If we choose 57 flares which soft X-ray telescope aboard Yohkoh started to observe before the HXR peak, X-ray plasma ejections are found in about 63-70% of these flares. We find X-ray plasma ejections in 100% of X-class flares and 74-82% of M-class flares, whereas only 31-38% of C-class flares have X-ray plasma ejections. It is difficult to detect X-ray plasma ejections in C-class flares, because the scale size is short and the lifetime of ejections is short. We propose that solar flares including microflares occur through magnetic reconnection, and that X-ray plasma ejections are general phenomena associated with solar flares. | |
| Presentor: | Olga Panasenco |
| Title: | YOHKOH LESSONS ABOUT DYNAMICAL LOOPS IN THE SOLAR CORONA: THE THEORETICAL VIEWS |
| Authors: | Panasenco, O.A. (Institute of Nuclear Physics, Moscow State University)
Veselovsky, I.S. (Institute of Nuclear Physics, Moscow State University) |
| Yohkoh observations revealed that a large number of active region transient loop brightenings (ARTB), which are presumably manifestations of torsional Alfven wave trains (TAWT) and that outermost structures of active regions contain lot of expanding loops likely to be driven by magnetic forces (Uchida, 2000). In addition, the diminishing loops and downflows are seen (not too often) in the Yohkoh/SXT and TRACE/EUV movies.
We suggest the theoretical interpretation of these phenomena, which develops ideas of dynamic current injections taking into account field-aligned and cross-field inductive electric current and electric fields with different space-time scales comparable to the characteristic lengths and durations of observed multi-scale phenomena (isolated lops and loop systems). Electric drifts in the crossed magnetic and inductive electric fields are important ingredients of the active loop dynamics. The dimensionless scaling approach is used to elucidate main possible cause-consequence chains, which are admissible at the present level of the observational knowledge and can be checked in future observations with a better resolution. | |
| Presentor: | Clare Parnell |
| Title: | Multispacecraft observations of quiet Sun transient events and X-ray bright points |
| Authors: | Parnell, C.E. (University of St. Andrews) |
| Over the last decade the unprecedented uninterrupted, high resolution, coverage of the Sun has led to the discovery of many new types of small-scale phenomena, as well as a better understanding of phenomena such as X-ray bright points and coronal plumes. Due to the excellent range of telescopes aboard the many spacecraft currently viewing the Sun these small-scale phenomena have been observed in many different wavelengths. Much has been discovered over the past 10 years, but there are still many questions to be answered. What are the connections between all these different small-scale transient phenomena? How are they created? Do they contribute to the heating of the solar corona and if so how significant is their contribution? Are any of them the source of the fast solar wind? I will be reviewing what has been discovered about both the new and well known dynamic quiet Sun phenomena from not only Yohkoh, but also SOHO and TRACE. In particular, I shall discuss the connections they appear to have to X-ray bright points and coronal plumes and will consider if any of them make a major contribution to the heating of the corona. | |
| Presentor: | Vahe Petrosian |
| Title: | Looptop Hard X-ray Emission and acceleration of Electrons in Flares |
| Authors: | Vahe, - (Petrosian)
Timothy, Q (Donaghy) James, M (McTiernan) |
| The discovery of hard X-ray sources near the top of a flaring loop by the HXT instrument on board the YOHKOH satellite represents a significant progress towards the
understanding of the basic processes driving solar flares. We have extended the previous study of limb flares by Masuda by including all YOHKOH observations upthrough August 1998. We find that from October 1991 to August 1998, YOHKOH observed 20 X-ray bright limb flares, of which we have sufficient data to analyze 18 events, including 8 previously unanalyzed flares. Of these 18 events, 14 show detectable impulsive looptop emission. Considering that the finite dynamic range of the detection introduces a strong bias against observing comparatively weak looptop sources, it can be conclude that looptop emission is a common feature of all flares. In this talk we will describe the light curves and images of some of the newly analyzed limb flares and will summarize the observations of the footpoint to looptop flux ratios and the spectral indices. The importance of these observations (and those expected from the scheduled HESSI satellite with its superior angular spectral and temporal resolution) in constraining acceleration models and parameters will also be discussed. | |
| Presentor: | Alexei Pevtsov |
| Title: | X-ray Bright Points and Photospheric Bipoles During Cycles 22 and 23. |
| Authors: | Sattarov, I. (Ulugh Beg Astronomical Institute of Uzbek Academy of Science)
Pevtsov, A. A. (National Solar Observatory, U.S.A.) Hojaev, A. S. (Ulugh Beg Astronomical Institute of Uzbek Academy of Science) Sherdonov, C. T. (Ulugh Beg Astronomical Institute of Uzbek Academy of Science) |
| Using daily Yohkoh SXT full disk images from 1991-2000 we manually identify X-ray bright points (XBPs). We also employ the NSO/KP full disk magnetograms from April 1992-June 2000 to identify the photospheric bipoles with particular magnetic flux and poles separation. We use these data to study statistical properties of XBPs and photospheric bipoles during declining phase of cycle 22 and rising phase of cycle 23. The number of X-ray bright points follows well-known anti-cycle variation, reaching a maximum in 1996 (sunspot minimum). By contrast, the averaged number of photospheric bipoles remains approximately the same during 1992-2000. We see this inconsistency between X-ray and magnetic data as clear indication that anti-cycle variation of XBP number is apparent, not real effect. | |
| Presentor: | Alexei Pevtsov |
| Title: | Sinuous Coronal Loops at the Sun. |
| Authors: | Pevtsov, A. A. (National Solar Observatory) |
| The sinuous coronal loops - sigmoids, first noted in the Skylab X-ray observations in association with a CME, - are commonly observed in Yohkoh soft X-ray telescope (SXT) data. The S-shape of these loops is a manifestation of the helical structure of the coronal magnetic fields and, hence, follows the hemispheric helicity (chirality) rule
established for quiescent filaments and photospheric magnetic fields. The forward-S (inverse-S) sigmoids prevail in southern (northern) hemisphere, independent of the solar cycle. Sigmoids are often associated with the CMEs; they exist prior to eruption and disappear after. In addition, active regions that exhibit sinuous loops are more likely to be eruptive than non-sigmoidal regions. Once erupted, sigmoids tend to produce stronger geomagnetic storms, and often the orientation of magnetic field in interplanetary disturbance can be directly linked to the coronal field of a sigmoid. In this talk we review the observational properties of sigmoids, current theoretical models and application of sinuous loops to space weather forecasting. | |
| Presentor: | Kenneth Phillips |
| Title: | Flare Temperatures from Fe XXV and Ca XIX: Refinements to Atomic Data |
| Authors: | Phillips, K.J.H. (Rutherford Appleton Laboratory (U.K.))
Rainnie, J.A. (Queen's University Belfast (U.K.)) Dubau, J. (Observatoire de Paris -- Meudon (France)) Keenan, F.P. (Queen's University Belfast (U.K.)) Harra, L.K. (Mullard Space Science Laboratory (U.K.)) |
| For several years flare temperatures and emission measures have been derived from comparison of observed Yohkoh BCS spectra with theoretical spectra derived from atomic parameters based on distorted wave approximation. In the case of Fe XXV and Ca XIX spectra, the main lines used in the determination are dielectronic satellite lines (j or k as appropriate) and the resonance line w. More accurate close-coupling calculations from the R-matrix procedure have been available in unpublished form, and in this work these new atomic data were substituted for the distorted wave data. The intensities of the Fe XXV and Ca XIX lines w, x, y, and z are affected -- all are increased. However, the differences from the previously used atomic data are very slight. We estimate that for a given j/w ratio in Fe XXV, for instance, the temperature estimated from the new atomic data will be about 1MK smaller than from the existing data in the standard Yohkoh software at temperatures of around 20MK. Smaller differences are expected for Ca XIX at typical temperatures of 14MK. The increase in the Fe XXV y and z line intensities tends to reduce a well-known discrepancy in these lines (more evident in the much better resolved SMM BCS spectra) but not by a sufficient amount to explain the discrepancy. | |
| Presentor: | Katharine Reeves |
| Title: | A Model for the Cooling of Post-Flare Loops |
| Authors: | Katharine, K (Reeves)
Harry, P (Warren) |
| We have developed a multi-thermal model for the cooling of post-flare loops.
The model consists of an arcade of many nested loops that reconnect and begin cooling at slightly different times, and have different cooling profiles because of the different loop lengths across the arcade. Cooling due to both conductive and radiative processes is taken into account. The free parameters in the model include initial temperature and density in the loop, loop width and the initial loop length. The results from the model are then compared to TRACE and SXT observations. Our many-loop model does a much better job of predicting the SXT and TRACE light curves than a similar model with only one loop. | |
| Presentor: | Eugene Romashets |
| Title: | Force Free Magnetic Structure Inside Toroid |
| Authors: | Romashets, E. P. (Institute of Terrestrial Magnetism, Ionosphere, and Radio Wa) |
| We present a general form of a solution of equation for force free magnetic field curl B = alpha B inside toroid with arbitrary large and small radii. The solution consists of a set of harmonics. To determine the real magnetic structure corresponding to a passage of magnetic cloud of toroidal shape, the field inside it is assumed to be nearly force-free, since the ratio of plasma and magnetic pressure (beta) is less than 0.1. As a rule, for such objects one must determine coefficients for each harmonics in the set. Profiles of B and Bz for the case of zero and first order will be shown and used for interpretation of May 1997 interplanetary event.
| |
| Presentor: | James Ryan |
| Title: | A Scintillating Plastic Fiber Tracking Detector for Solar Neutron Imaging and Spectroscopy |
| Authors: | Ryan, J.M. (UNH)
Macri, J.R. (UNH) McConnell, M.L. (UNH) Messner, R. (UNH) Cutlip, H. (UNH) Castaneda, C. (UCD) Romero, J.L. (UCD) |
| We report the results of recent calibrations of a prototype scintillating fiber tracking detector system designed to perform imaging and spectroscopy of solar neutrons from 20 to 250 MeV. We present the neutron imaging concept and briefly review the detection principle and the prototype description. The detector system records ionization track data on an event-by-event basis allowing event selection criteria to be used in the off-line analysis. Images of acrylic phantoms from the analysis of recent proton beam calibrations (14 to 65 MeV) are presented to demonstrate the intrinsic resolving power of the instrument. The measured position resolution is < 500 microns. The measured energy resolution (deltaE/E, FWHM) is 14.2% at 35 MeV. An effective technique for track identification and data compression is presented. | |
| Presentor: | James Ryan |
| Title: | Gamma-Ray Measurements of the 15 November 1991 Solar Flare |
| Authors: | Ryan, J.M. (UNH)
Arndt, M.B. (Bridgewater State College) |
| This event was well observed by Yohkoh, Compton and ground-based observatories. Gamma rays were detected up to 8 MeV indicative of an accelerated ion spectrum containing at least 10^27 ergs with a spectrum of E^(-4.5). This amount of energy is not sufficient to produce the detected white light emission. The ions also produced neutrons that in turn generated 2.223 MeV gamma-ray emission. The time decay of this emission is unusually rapid (26 s) suggesting an elevated abundance of 3He assuming the absence of much higher energy particles. | |
| Presentor: | Julia Saba |
| Title: | A study of magnetic reconnection using simultaneous SOHO/MDI and TRACE data |
| Authors: | Saba, J.L.R. (LMSAL at NASA/GSFC)
Gaeng, T. (Emergent IT Inc. at NASA/GSFC) Tarbell, T. D. (Lockheed Martin Solar & Astrophysics Lab) |
| High-resolution, high-cadence images from the Transition Region and Coronal Explorer (TRACE) together with high quality magnetograms from the Michelson Doppler Imager (MDI) on SOHO let us examine signatures of magnetic reconnection and attempt to infer associated physical parameters such as the electric field strength in the corona.
We analyzed TRACE UV and MDI magnetogram data for a two-ribbon, GOES M1-class flare from NOAA active region 9236 at 2000 Nov 23 23:28 UT, with emphasis on the dynamical development of the flare ribbons in the TRACE images. To estimate the rate of magnetic reconnection, we chose two obvious flare ribbons which grew rapidly in the first 290-second sequence of high-cadence 1600,AA flare response images. These ribbons could be separated with a simple binary mask from ejecta and other emission. They were located on strong fields of opposite polarity and grew rapidly, then faded away in place. This suggests that the emission was low in the atmosphere and well-aligned with the photospheric footpoints of fieldlines reconnecting in the corona. Thus we assume that the reconnection rate can be determined from the changing photospheric magnetic flux swept out by the evolving ribbon mask. The reconnection rate is very noisy, with a correlation time of at most a few seconds. For simple assumptions with standard coronal parameters ($B sim 100$ G, $n_p sim 3 imes 10^9 , { m cm}^{-3}$ near a strong sunspot), the reconnection appears to be fast, with the inferred inflow velocity a significant fraction of the Alfven velocity. Some guidance from coronal imaging of the reconnection region or Doppler measurement of inflow is needed to sharpen the constraints on the length of the reconnecting current sheet and the strength of the coronal electric field. This work was supported by NASA contracts NAG5-8878, NAG5-10483 (MDI) and NAS5-38099 (TRACE). | |
| Presentor: | Takashi Sakurai |
| Title: | Spectroscopic Observation of Coronal Oscillations |
| Authors: | Sakurai, T. (National Astronomical Observatory of Japan)
Ichimoto, K. (National Astronomical Observatory of Japan) Raju, K.P. (Indian Institute of Astrophysics) Singh, J. (Indian Institute of Astrophysics) |
| A time-sequence of coronal spectra has been obtained in
the green line [FeXIV] 5303 {AA} at the Norikura Solar Observatory. The slit was placed perpendicular to the solar limb, and the data were taken with 25 s cadence for about 80 minutes. Emission line intensities, Doppler velocities, and line widths have been obtained through fitting a single Gaussian to the observed line profiles. Coronal oscillations have been detected at localized regions. Oscillations have been found to be prominent in Doppler velocities, while weak oscillations were seen in line widths and intensities. Power spectral analysis of the time sequence gives the period of oscillations. Significant periodicities are seen in the range of 2--8 mHz. The phase lag of Doppler oscillation between points along the slit indicates the existence of propagating waves whose speed is a few hundred km s$^{-1}$. | |
| Presentor: | Jun Sato |
| Title: | Flare analysis using YOHKOH (SXT, HXT) and HESSI data |
| Authors: | Sato, J (Montana State University) |
| I have used soft and hard X-ray images obtained from Soft X-ray Telescope (SXT) and Hard X-ray Telescope (HXT) onboard Yohkoh to study loop-top source during an interesting flare for which the footpoints are occulted. The results show: (1) The existence of an extended nonthermal source located in the higher corona (h $sim$ 50000 km). (2) Dominant thermal and nonthermal sources do not come from the same loop-top region. Based on these results, we discuss studies to be made using the forthcoming High Energy Solar Spectroscopic Imager (HESSI) satellite. HESSI will be launched this autumn. It will be the first instrument to observe hard X-rays with high spatial (about 2 arcsec) and spectral (about 1 keV FWHM) resolution.
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| Presentor: | Hanumant Sawant |
| Title: | Harmonically related zebra patterns in (1- 4)GHz frequency ranges in June 6, 2000 flare. |
| Authors: | Sawant, H.S. (Instituto Nacional de Pesquisas Espaciais)
Karlicky, M. (Ondrejov Observatory of Republic Checa) Fernandes, F.C.R. (Instituto Nacional de Pesquisas Espaciais) Cecatto, J.R. (Instituto Nacional de Pesquisas Espaciais) |
| Long lasting X2.3 flare was recorded on radio waves from 15:00 till 17:00 UT on
6th June 2000. A full-halo coronal mass ejection and type II bursts were associated with this flare. This flare is rich in zebra patterns above 1000 MHz. For the first time we are reporting harmonically related zebra structures above 1000 MHz, having ratio of 1:2. Zebra structures show up to 8 zebra lines. In individual zebra patterns the frequency ratio of the neighbouring zebra lines are less than 1.03 and these ratios decrease with the frequency decrease. The zebra patterns are analysed and interpreted assuming double plasma resonance instability as the cause for their generation. The longitudinal upper hybrid waves are excited at positions of cyclotron resonance and then transformed into electromagnetic ones. Using this model the magnetic field strengths ,in the flaring loops, are estimated and are in the range of 110-230 G. | |
| Presentor: | Hanumant Sawant |
| Title: | Decimetric Reverse Drift and U type Bursts in the April 9,2001 Flare |
| Authors: | Cecatto, J.R. (National Institute for Space Research)
Sawant, H.S. (National Institute for Space Research) Fernandes, F.C.R. (National Institute for Space Research) Krishan, V. (National Institute for Space Research) Rosa, R.R. (National Institute for Space Research) Karlicky, M. (Ondrejov Observatory) |
| We report a long duration (~27 min.) radio emission in the frquency range 0.8-3.0 GHz beginning at ~ 15:25 UT on April 9,2001,recorded jointly by the Brazilian Solar Spectrograph(BSS) and the Ondrejov Radio Observatory..The spectra of the emission consist of continuum as well as the bursty emission. The bursty component is made up of the U type as well as the Reverse Drift (RS) bursts.The emission region of the bursts has been identified by using the SOHO data from which the dimensions of the emitting coronal loop have been determined.A knowledge of the duration of the U bursts then enables us to determine the speed of its exciting agency.The speed so derived is suggestive of the magnetohydrodynamic(MHD) shocks that are generally believed to be responsible for type 2 like radio bursts.From the measured drift rates of the RS bursts, assuming a power law coronal density model , the speed of the exciting agency of the RS bursts turns out to be comparable to that of the U burst, perhaps implying a common shock associated emission mechanism. | |
| Presentor: | Edward Schmahl |
| Title: | Imaging High Energy Flares with HESSI |
| Authors: | Schmahl, E. (NASA GSFC and Astronomy Dept., Univ. of MD)
Conway, A. (Dept. Physics and Astronomy, The Open University) Sato, J. (Dept. Physics, Montana State University) Aschwanden, M. (Lockheed Martin Advanced Technology Center) Metcalf, T. (Lockheed martin Advanced Technology Center) Schwartz, R. (Lab for Astronomy and Solar Physics, NASA GSFC) Krucker, S. (Space Science Lab, UC Berkeley) |
| The High Energy Solar Spectroscopic Imager (HESSI) will use rotational modulation synthesis for mapping hard X-ray and gamma-ray flares with spatial resolution of 2.3'' and spectral resolution of ~ 1 keV. Like the Yohkoh/HXT hard X-ray telescope, HESSI relies on Fourier techniques to make images, but HESSI has many more sampling points in the Fourier plane, and is expected to produce higher resolution maps with greater dynamic range.
We summarize 7 methods to be used for HESSI imaging: Back-Projection, CLEAN, Visibility Maximum Entropy, Count-rate MEM, Pixelized and Unpixelized Forward Fitting, and PIXONs. All of these methods are available to the user community through the Solar Software Tree. We present examples of simulated images, with estimates of the imaging photometry and the required computer resources for each technique. | |
| Presentor: | Michal Sersen |
| Title: | Flaring in Multipolar Regions on the Sun: Initial Study |
| Authors: | Sersen, M. (Comenius University, Bratislava, Slovak Republic) |
| Several H-alpha flares which were observed with a new H-alpha Telescope at the Modra Astronomical Observatory in Slovakia are analyzed in this presentation. Multiwavelength data from ground-based instruments and Yohkoh/SXT show that multiple loops are involved in these flares. The magnetic configuration in the flaring regions is always multipolar rather than bipolar. The situation is consistent with the scenario of new-emerging small-scale loops that reconnect with pre-existing large-scale loops. This presentation is an introduction to an extensive study of flaring in multipolar regions based on SoHO/MDI and Yohkoh/SXT observations. | |
| Presentor: | Kazunari Shibata |
| Title: | Observations of Moreton Waves and EIT Waves |
| Authors: | Shibata, K (Kwasan and Hida Observatories, Kyoto Univ.)
Eto, S (NONE) Narukage, N (NONE) Isobe, H (NONE) Morimoto, T (NONE) Kozu, H (NONE) Asai, A (NONE) |
| The Moreton wave is a flare-associated wave observed in
H alpha, and is now established to be a fast mode MHD shock emitted from the flare, but the physical mechanism to create the wave is still puzzling. On the other hand, the EIT wave is a newly discovered flare-associated wave observed in EUV with the Extreme ultraviolet Imaging Telescope (EIT) aboard SOHO, and in this case, not only its origin but also its physical property are both puzzling. We study the relationship of these two flare-associated waves, Moreton waves and EIT waves, by analyzing 4 events observed on Nov. 3 and 4, 1997, Aug. 8, 1998, and Mar. 3, 2000 (Narukage et al. 2001). The Moreton waves were observed in Ha, Ha+0.8A and Ha-0.8A with the Flare Monitoring Telescope (FMT) at the Hida Observatory of Kyoto University, while the EIT waves were observed with SOHO/EIT. In the typical case associated with an X-class flare in AR 8100 on 4 November 1997 (Eto et al. 2001) the propagation speeds of the Moreton wave and the EIT wave were approximately 780 km/s and 200 km/s respectively. The data on speed and location show clearly that the Moreton wave differs physically from the EIT wave in this case. The detailed analyses of the other events (Nov. 3, 1997, Aug. 8, 1998, and Mar. 3, 2000) will also be presented, with Yohkoh/SXT data in the lucky case. | |
| Presentor: | Toshifumi Shimizu |
| Title: | Connection Between Photospheric Magnetic Fields and Coronal Structure/Dynamics |
| Authors: | Shimizu, T. (National Astronomical Observatory) |
| Continuous observations of the solar X-ray corona with Yohkoh Soft X-ray Telescope (SXT) have been revealing that dynamical phenomena, such as coronal jets and microflares (transient loop brightenings) are common in the corona, especially in the active-region corona. Moreoever, the heating of the corona is about two order of magnitude
more significant in the active regions than in the quiet regions. Since observations of magnetic fields at the photosphere show that magnetic fields are much more concentrated into active regions, it has been widely believed that magnetic fields would be responsible for the heating of the corona as well as dynamics in the corona. A lot of complicated magnetic activities are observed at the photosphere; newly emerging magnetic fields, marging to the same-polarity magnetic fields, cancelling magnetic fields with the opposite-polarity magnetic fields, developing the shear in magnetic field structure, and so on. How are these magnetic activities associated with the dynamics and heating well observed in the coronaNULL A lot of investigations have been made by comparing Yohkoh observations with observatoins of photospheric magnetic fields. This paper reviews some of investigations made in the last decade. Solar-B is now under development for the launch scheduled in 2005. Its primary objective is to study the connection of the dynamics and heating observed in the solar corona with the magnetic field at the solar surface. For great advances in understanding the magnetic connection between the photosphere and the corona with Solar-B, it is significant important to review the recent knowledges obtained in the Yohkoh era. | |
| Presentor: | Masumi Shimojo |
| Title: | The temperature analysis of Yohkoh/SXT data using the CHIANTI spectral database |
| Authors: | Shimojo, M (NSRO/NAOJ)
Hara, H (NAOJ) Kano, R (NAOJ) |
| The atomic database for the emission lines is very important for the temperature analysis of Yohkoh/SXT since we derived the temperature of solar plasma using the model X-ray spectrum based on the database. Recently, Dere et al. (2001) made the atomic database for X-ray emission lines and released the new version of the CHIANTI package (Version 3). We calculated the temperature responses of the SXT analysis filters using the new CHIANTI package, and compared the results of temperature analyses based on the CHIANTI database with that based on the Mewe
database which is the standard database of YOHKOH/SXT. We found that the temperature analysis based on the Mewe database derived heigher temperatures than that based on the CHIANTI database. Especially, the temperature analysis using the Al.1/Al12 filter combination is influenced by the difference of these databases, and we found that the difference of the temperatures between Mewe and CHIANTI is 30-40% at 4-5MK.The Al.1/Al12 filter combination is one of the most usual combination for the temperature analysis of SXT data. Hence, there is the possibility that the previous analysis over-estimated thermal energy, the flux of thermal conduction and the flux of radiative loss of flares and active regions. | |
| Presentor: | Junho Shin |
| Title: | The Point Spread Function of Yohkoh Soft X-Ray Telescope |
| Authors: | Shin, J. (National Astronomical Observatory of Japan)
Sakurai, T. (National Astronomical Observatory of Japan) |
| Due to a finite width of the point spread function (PSF) of Yohkoh Soft X-Ray Telescope (SXT), it is expected that a certain amount of blurring effect is inherent in the observed images. Especially for flaring regions, it is necessary to remove these blurred components by deconvolution for both morphological and photometric purposes. Though there have been many attempts to determine the SXT PSF using various methods, we believe that the results were not satisfactory in describing the pattern of blurring. In this study we have analyzed the ground-based pre-launch test data of SXT and measured the shape of the PSF. We have found several reasons why this PSF could not be determined properly when normal fitting methods were applied. In particular, it is crucial that the effects of undersampling and noise in the data are treated properly.
Analyses made in the past have suggested that the SXT PSF varies with the position in the focal plane. It is very important to understand this spatial variation of the PSF because coronal activities usually happen not only on the disk center but also on the limb area of the sun. We will also report the degree of spatial variation of the SXT PSF across the focal plane. | |
| Presentor: | Gregory Slater |
| Title: | An Efficient and Versatile Video Server System For Studying the Yohkoh Mission Archive |
| Authors: | Bartus, J (Solar Physics Research Corporation)
Slater, G L (Lockheed Martin Solar and Astrophysics Laboratory) |
| We have developed a modest video server system and interface which will allow users to easily access and view the entire SXT full frame mission archive in video format, to generate movie sequences in real time, and to output such movies in DVD format, all at full spatial and intensity resolution. We have created sample data products using this system which demonstrate its usefulness.
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| Presentor: | Alphonse Sterling |
| Title: | SXT and EIT Observations of Quiet Region Large-Scale Eruptions: Implications for Eruption Theories |
| Authors: | Sterling, A. C. (MSFC/NSSTC/UAT)
Moore, R. L. (MSFC/NSSTC) Thompson, B. J. (GSFC) |
| We present Yohkoh/SXT and SOHO/EIT observations of a set of slow, large
scale, quiet-region solar eruptions. In SXT data, these events seem to appear ``out of nothing,'' indicating that they are associated initially with weak magnetic fields and corresponding low heating rates. These events evolve relatively slowly, affording us an opportunity to examine in detail their development. We look for signatures of the start of the eruptions through intensity variations, physical motions, and dimming signatures in the SXT and EIT data. In particular, we look to see whether the earliest signatures are brightenings occurring in the ``core'' region (i.e., the location where the magnetic shear is strongest and the post-flare loops develop); such early brightenings in the core could be indicative of a ``tether-cutting'' process, whereby the eruption is instigated by magnetic reconnection among highly-sheared core fields. In our best-observed case, we find motions of the core fields beginning well before brightenings in the core. This is new evidence that tether-cutting is not the primary mechanism operating in solar eruptions. Rather, our observations are more consistent with the eruption process known as the ``breakout model'' (Antiochos et al. 1999), which holds that the eruption results from initial slow magnetic reconnections occurring high above (far from) the core region. | |
| Presentor: | Peter Sturrock |
| Title: | Comparative Analysis of GALLEX-GNO Neutrino Data and SXT X-Ray Data |
| Authors: | Sturrock, P.A. (Stanford University)
Weber, M.A. (Stanford University) |
| There is some evidence that the low-energy component of the solar neutrino flux exhibits rotational modulation. The power spectrum of the GALLEX-GNO neutrino data has a peak at 13.59 +/- 0.06 y-1 (period = 26.88 +/- 0.12 days), that is within the band of synodic rotation rates of the solar convection zone. In order to relate the neutrino time series to the Sun's internal rotation, we have formed a "resonance statistic" that is a measure of the degree of "resonance" of the neutrino flux with the Sun's internal rotation, as determined by MDI. A map of this statistic indicates that the source of the modulation of the solar neutrino flux is located deep in the convection zone. We have now carried out a comparative analysis of GALLEX-GNO neutrino data and SXT X-ray data. We have formed the logarithm of the mean daily X-ray flux (to de-emphasize active regions) and then formed the mean power spectrum for five 15-degree latitude bands centered on 30S, 15S, the equator, 15N, and 30N. The mean spectrum peaks at 13.54 +/- 0.08 y-1 (period = 26.98 +/- 0.16 days). Taking account of the error bars, the neutrino peak frequency and SXT peak frequency are indistinguishable. We find that the neutrino and X-ray waveforms are approximately in anti-phase. We have also formed a map of the resonance statistic formed from the SXT power spectrum and the MDI rotation estimates. The neutrino-rotation and X-ray-rotation resonance maps are very similar, and both point to the same location deep in the convection zone. These results suggest that modulation of the low-energy solar neutrino flux and long-lived quasi-rigid rotation of the corona have a common cause. It seems possible that a magnetic structure deep in the convection zone leads to (a) an enhancement of the X-ray flux, and (b) a diminution of the observed neutrino flux. This diminution could be caused by any one of several proposed mechanisms by which an electron neutrino, with non-zero magnetic moment and non-zero mass, may be converted into a neutrino of different flavor and/or opposite spin. | |
| Presentor: | Barbara Sylwester |
| Title: | High Resolution Observations of Solar Flares |
| Authors: | Sylwester, B. (Space Reseach Centre, Polish Academy of Sciences) |
| The most suitable data set available for investigation of flares has been accumulated by the Yohkoh instruments. The SXT collected a wealth of solar X-ray images including thousands of flare sequences.
Over several past years, our team in Space Research Center (SRC) of Polish Academy of Sciences in Wroclaw has been interested in developing the numerical image enhancement techniques with the aim of increasing the resolution on SXT flare images. The algorithm has been worked out which allows for the image deblurring with oversampling. The code (ANDRIL) is available in the public domain (SolarSoft). The application of this algorithm allows to increase the resolution on the SXT images to the level of ~1 arc sec. We performed the deconvolution of large number of flare sequences using ANDRIL algorithm. The analysis of these data allowed to study the morphology of million degree flaring plasma with the resolution comparable to TRACE. The main results will be presented in the review. In order to infer the thermodynamic parameters of the plasma from the analysis of deconvolved images their precise coalignment is required. Techniques which have been developed at SRC to achieve high accuracy of image coalignment will be presented. The application of filter ratio (Al12/Be119) technique to the deconvolved and coaligned images allows to study temperature and emission measure distributions in great details. These maps better resolve flare kernels located both at the summits and foot points of flaring loop structures. We have studied the thermodynamic properties of kernels and related them with the corresponding characteristics derived from the analysis of BCS and HXT data. Performed analysis improved considerably our understanding of solar flares. Many of the results and theoretical ideas presented in this review have been obtained in cooperation with the team from the Astronomical Institute of Wroclaw University. | |
| Presentor: | Janusz Sylwester |
| Title: | Behind the Limb X-ray Sources as Seen by the Yohkoh |
| Authors: | Sylwester, J. (Space Research Centre, Polish Academy of Sciences)
Sylwester, B. (Space Research Centre, Polish Academy of Sciences) |
| It is known, that the application of filter ratio (Al12/Be119) technique into the analysis of SXT images requires a precise image coalignment. The coalignment problems are even more serious in the case of analysis of deconvolved images with oversampling. In order to achieve the necessary alignment accuracy in this case, we have used the occulting solar limb position as a reference. The limb's position, as seen on images taken using individual SXT filters, may depend on the source temperature and the filter transmission. We have investigated this dependence using VAL model of the photosphere/chromosphere transition region. We have found a difference of ~ 0.3 arcsec (200 km) of the limb location as seen on images taken with Be119 and the other SXT filters. The difference is even larger for individual HXT channels. Results of the analysis allow us to coalign the Al12 and Be119 deconvolved images to the required accuracy. In parallel, we also discuss implications of the occultation phenomenon on the shape of X-ray lightcurves for kernels evanescent from behind the limb.
By applying filter ratio (Al12/Be119) technique to deconvolved images we have studied the evolution of temperature and emission measure of flaring kernels with ~1 arcsec resolution for behind the limb sources. Obtained high resolution temperature and emission measure maps we have compared with the maps of hard X-ray brightness (HXT). We discuss physical implications of the results obtained. | |
| Presentor: | Aki TAKEDA |
| Title: | Evolution of the 'gorgeous coronal hole' |
| Authors: | TAKEDA, A. (SPRC/ISAS)
KUBO, S. (ISAS) |
| A distinct coronal hole was observed in the final quarter of the last year, (October - December, 2000), at around 180 degrees in the Carrington Longitude. Observed with SXT, the coronal hole had an elongated shape in the north-south direction across the equator, held its outline for at least three rotations (C.R. 1968 - 1970), and broke into three pieces to disappear in January, 2001. In this presentation, we will closely describe the formation through decay of this 'gorgeous' coronal hole, based on a series of SXT images, the synoptic magnetic-field charts given by Kittpeak, and other satellite images taken with TRACE and SoHO. During the October rotation, this hole was in a similar shape to the Italian Peninsula, which reminds us of the famous coronal hole, CH1, observed by Skylab (June - October, 1973). However, it turns out that the 'gorgeous' hole is different from the CH1 in the following two aspects. (1) Although the 'gorgeous' hole appears to connect with the north pole in SXT images, it has a negative polarity, the opposite of the actual polarity of the north pole. Thus, the 'gorgeous' hole is not a polar-hole extension like CH1. (2) The 'gorgeous' hole originated from the active regions that emerged during a few rotations before (around C.R.1965) and rotated at the local rate according to their latitude. This falls into the category of 'sheared extensions' introduced by Wang and Sheeley (1993), not the 'rigid extensions' like CH1. | |
| Presentor: | Akitsugu Takeuchi |
| Title: | PROPERTIES OF MAGNETIC RECONNECTION IN A STRATIFIED ATMOSPHERE |
| Authors: | Takeuchi, A. T. (Yonago National College of Technology)
Shibata, K. S. (Kwasan Observatory, Kyoto University) |
| We study properties of magnetic reconnection in a
stratified atmosphere such as the solar photosphere, performing 2--dimensional magnetohydrodynamic (MHD) numerical simulations. The reconnection is caused by an encounter of oppositely directed vertical magnetic flux sheets, where the initial sheets are calculated assuming the thin flux tube approximation. We adopt a resistivity model in which the resistivity is described as a function of height with a maximum (where the magnetic Reynolds number = 2000) at a middle height of our simulation box, because the actual solar resistivity possesses a maximum at the temperature--minimum region. Owing to the resistivity, magnetic reconnection occurs around the middle and evolves into reconnection with slow mode MHD standing shock waves like the Petschek type reconnection. We investigate asymmetry of the upward and downward reconnection jets. It is found that the velocities of the upward and downward jets are faster and slower than the Alfv'{e}n velocity, respectively. Moreover, temperature of the upward jet is cooler than that of the downward jet. The asymmetry of mass, momentum, and energy carried by the jets are discussed. The inflow speed to the reconnection region ($v_{i} sim$ 160 m/s) is nearly equal to the speeds implied by observations of canceling magnetic features on the photosphere. Thus photospheric magnetic reconnection seems to be a cancellation mechanism. | |
| Presentor: | Syuniti Tanuma |
| Title: | The Structure of Magnetic Reconnection Jet: Three-Dimensional Numerical Magnetohydrodynamic Simulations |
| Authors: | Tanuma, S (Kwasan Observatory, Kyoto University)
Yokoyama, T (Nobeyama Radio Observatory) Kudoh, T (National Astronomical Observatory) Shibata, K (Kwasan Observatory, Kyoto University) |
| We study the magnetic reconnection jet
by performing three-dimensional(3D) MHD simulations. We found that the magnetic reconnection starts long after the shock wave (fast-mode MHD shock) passes a current sheet. In 2D models, the current sheet evolves as follows: (i) Tearing-mode instability is excited by the shock wave, and the current sheet becomes thin in its nonlinear stage. (ii) The current-sheet thinning is saturated when the current-sheet thickness becomes comparable to that of Sweet-Parker current sheet. After that, Sweet-Parker type (slow) reconnection starts, and the current-sheet length increases. (iii) ``Secondary tearing-mode instability'' occurs in the thin Sweet-Parker current sheet. (iv) As a result, further current-sheet thinning occurs and anomalous resistivity sets in, because the gas density decreases in the current sheet just after the plasmoid is ejected. Petschek type (fast) reconnection starts and heats the gas. The magnetic energy is released quickly while the magnetic islands are moving in the current sheet during Petschek type reconnection. The released magnetic energy is determined by the magnetic field strength, not energy of initial explosion, nor distance between the explosion and current sheet (i.e., the initial explosion is only a perturbation). By performing 3D simulations, we study 3D effects on the dissipation regions and reconnection jet. We will show details of 3D structure of reconnection jet. | |
| Presentor: | Theodore Tarbell |
| Title: | La Palma and TRACE Observations of Chromospheric Responses to Reconnection |
| Authors: | Tarbell, T D (LMSAL) |
| Recently, several groups have studied the time evolution of
flare ribbons in the chromosphere, transition region, or low corona. When coaligned magnetograms are also available, estimates of the magnetic reconnection rate can be made. In this talk, I present observations of this type with very high spatial resolution obtained at La Palma in 1992, with simultaneous SXT and HXT observations of an M1 flare. Several wavelengths in H-alpha and longitudinal magnetograms show the early progress of a ribbon through regions of low magnetic flux density for more than half an hour before the impulsive phase of the flare. Beautiful fine structures in the emission kernels are seen in the far blue wing of H-alpha; their correspondence with photospheric fields and hard X-rays is discussed. Other examples using TRACE movies with MDI magnetograms are shown briefly. | |
| Presentor: | Evgeniy Tikhomolov |
| Title: | Excitation of the mid- and low-latitude Rossby vortices at the base of the solar convection zone and formation of the complexes of activity |
| Authors: | Evgeniy Tikhomolov, (TRIUMF, Canada's National Laboratory) |
| According to a number of researches solar differential rotation on time-scale of several years is stable in mid- and low latitudes both in the bulk and at the base of the solar convection zone. On the other hand solar torsional waves revealed by Howard and LaBonte evidence the existence of oscillations of the differential rotation in high latitudes. We show how the oscillations of the shear in high latitudes produce the shear waves traveling to low latitudes, i.e. torsional waves. Due to shear waves the differential rotation in mid- and low- latitudes at the base of the solar convection zone becomes unstable during short period of time on the order of half a year and large-scale Rossby vortices appear. Rossby vortices are the effective source of such long-lived large-scale formations as complexes of activity. Numerical simulations of the various processes that lead to the formations of the complexes of activity and large sunspots are presented. | |
| Presentor: | Yutaka Uchida |
| Title: | Bubble-Type CME as due to Flare Blast, and Loop-Type CME as due to the Drive by the Magnetic Twist Released into Reconnected large Loop --- Observations and Models --- |
| Authors: | Uchida, Y (Science University of Tokyo)
Cameron, R (Science University of Tokyo) Kuwabara, J (Science University of Tokyo) Tanaka, T (Science University of Tokyo) Hata, M (Science University of Tokyo) Suzuki, I (Science University of Tokyo) |
| We claim that there are, at least, two distinctly different types among CME's, one with a bubble type shape expanding roughly isotropically in association with explosive flares, and the other with a large loop type shape whose anchoring point in the middle is released in an arcade flare occurring in between the footpoints. The former is found to be associated with EIT wave, but almost constant velocity of its expansion is significantly greater than that of the associated EIT wave. The motion of the latter, the loop-type, is more characteristic with acceleration and deformation of the loop shape, but the most notable is that the footpoints are fixed, whereas the footpoints can not stay fixed in the bubble-type. Recent impactful discovery about the EIT wave was that it turned out to be different from the Moreton wave which people tended to identify with EIT wave. Moreton wave was found to propagate separately with significantly greater velocity than EIT wave. We showed by using 3D MHD simulations that the bubble-type CME may be identified with the flare-blast wave front whose skirt sweeps on the chromosphere as Moreton wave. We interpret EIT wave as due to a secondary long wavelength fast-mode wave caused by the flare-associated gas motion, and trapped in the propagation trough in the low corona. This propagates with a slower velocity due to the nature of the wave trapped in the trough, and couples more easily with the slow-mode gas motion at the resonating layer of the fast and slow waves in the high chromosphere. This coupling supplies the heated gas to the low corona. We propose separately an MHD model for loop-type CME's based on our finding of the pre-event connections between their footpoints and associated arcade flare between them. The acceleration and the deformation of the loop shape are attributed to the drive and helical instability due to the injection of the magnetic twists into the reconnected large loop cut off from the flare region. | |
| Presentor: | Lidia van Driel-Gesztelyi |
| Title: | Helicity loading and dissipation: the helicity budget of AR 7978 from the cradle to the grave |
| Authors: | van Driel-Gesztelyi, L. (MSSL, University College London, RH5 6NT, UK)
D'emoulin, P. (Observatoire de Paris, DASOP, 92195 Meudon Cedex, France) Mandrini, C.H. (IAFE, CC.67, Suc.28, 1428 Buenos Aires, Argentina) Thompson, B. (NASA/Goddard SFC, Greenbelt, MD 20771, USA) Plunkett, S. (Naval Research Laboratory, Washington, DC 20375, USA) KH{o}v'ari, Zs. (Konkoly Observatory, Budapest, Pf. 67, H-1525, Hungary) Aulanier, G. (Observatoire de Paris, DASOP, 92195 Meudon Cedex, France) |
| An isolated active region was observed on the Sun during seven
rotations, starting in July 1996. I will present a study of its magnetic field, concentrating on its helicity budget. The photospheric field is extrapolated into the corona in a linear force-free approach, using SOHO/MDI magnetograms and Yohkoh/SXT images, allowing us to compute, in a crude way, the relative coronal magnetic helicity of the active region. Using the observed magnetic field distribution (SOHO/MDI magnetograms) we also calculate the helicity injected by the differential rotation during seven solar rotations. Finally, using SOHO/LASCO and EIT as well as Yohkoh/SXT observations, we identify all the 26 CMEs which originated from this active region during its lifetime and using average values of the field and radius of magnetic clouds, we estimate the helicity which should be shed via CMEs. We compare these three values to evaluate the importance of the differential rotation relative to twisted flux emergence as a source of magnetic helicity. We find that the differential rotation can neither provide enough helicity to account for the diagnosed coronal heicity values, nor for the helicity carried away by CMEs. We suggest that the main source of the magnetic helicity must be the inherent twist of the magnetic flux tube forming the active region. This magnetic helicity is transferred to the corona either by a slow continous emergence of the flux tube or by torsional Alfven waves, during several solar rotations. | |
| Presentor: | Hari Vats |
| Title: | Coronal mass ejections and interplanetary scintillation |
| Authors: | Vats, H O (PRL India and INPE Brazil)
Jadhav, R M (SU Rajkot India) Iyer, K N (INPE Brazil and SU Rajkot India) Sawant, H S (INPE Brazil) |
| Excellent set of observations of coronal mass ejections are now available from Yohkoh and SOHO. It has become possible to investigate the initial ejection and acceleration of these from the X-ray images. The monitoring of propagation of the coronal mass ejections away from the Sun in the heliosphere is only possible by an indirect method of interplanetary scintillation (IPS). This phenomenon is sensitive to the presence and propagation of plasma irregularities crossing the line of site to a compact radio source from the observing radio telescope. The passage of a coronal mass ejection through the heliosphere is usually termed as interplanetary disturbance (IPD). Here we present the case studies of few selected coronal mass ejections and their associated IPDs. One of these a halo CME with a bright front (as seen in SOHO/LASCO) began on April 04, 2000 at about 1632 UT. This was associated with C9 flare in AR 8933. The IPS observations at 103 MHz detected the effect of this CME two days later at the line of sight of 3C459 and three days later at the line of sight of 3C2, 3C119 and 3C122. At the line of sight of 3C48 there appeared a very feeble effect of this CME. The CME of April 4, 2000 produced a shock which was detected by ACE solar wind velocity measurement (the radial velocity increased from 375 km/sec to 575 km/sec at 16 UT on April 6, 2000). We will compare shock magnitude with acceleration measured by SOHO images of the CME. This shock led to a very large drop (about 300 NT) in equatorial Dst and produced one of the largest geomagnetic storm. Here we will discuss these events in complete detail from their origin at Sun up to their interaction with the terrestrial environment. We will also inter compare the terrestrial impact of these events observed by IPS. | |
| Presentor: | V. VERMA |
| Title: | RELATIONSHIP OF HALO CORONAL MASS EJECTIONS WITH SOLAR ACTIVE PHENOMENA, COROMNAL HOLES AND GEOMAGNETIC STORMS |
| Authors: | VERMA, V. K. ( STATE OBSERVATORY, NAINITAL-263129, INDIA) |
|
In the paper we present the study of relationship of halo coronal mass ejection (HCME) events with solar activity phenomena, coronal holes(CHs) and geomagetic storms. Out of 119 HCME events observed between the period February, 2000 - October, 2001, only 114 HCME events are related with solar activity phenomena. Further, out of 114 HCMEs, corresponding to only 96 HCMEs the CHs data are available. From the study of 96 HCMEs, we have found that about 42\% HCMEs were observed when there are CHs within 10 degrees from the location of solar H-alpha or EIT phenomena and 22\% HCMEs were observed when there are CHs within 11-20 degrees from the location of solar H-alpha or EIT phenomena. Further, 20\% HCMEs were observed when there are CHs present within 21-30 degrees from the location of solar H-alpha or EIT phenomena. We found that sometimes when the minimum distance between the location of solar phenomena and boundry of CHs are small the intensity of geomagnetic storms are high. Our study also show that all the HCMEs does not produce geomagnetic storms as reported earlier by Cane et al (2000). References:- Cane, H.V.,Richardson, I. G. & St. Cyr, O. C.:2000, Geophysical Research Letter, 27, 3591. | |
| Presentor: | V. VERMA |
| Title: | Coronal Mass Ejection's relationship with Solar Flares and Coronal Holes |
| Authors: | Verma, V. K. (State Observatory, Nainital-263129, India) |
| The results of an analysis of the relationship of coronal mass ejections (CMEs) with solar flares and coronal holes are presented. In the present study CME's observed by LASCO coronagraph and whose locations were identified by EIT instruments and solarH-alpha flares during year 2000 are used in the present study. The coronal holes data used in study were observed by KPNO, USA. From the study we have found that about 40% CMEs were observed when there were coronal holes within 10 degrees from the location of solar H-alpha flares and 25% CMEs were observed when there were coronal holes within 20 degrees from the location of solar H-alpha flares. Further, 30% CMEs were observed when there were coronal holes present within 21-40 degrees from the location of solar H-alpha flares. The present work supports the view that the origin of CME's has a relationship with coronal holes in close vicinity as suggested by Verma and Pande (1989) and Verma(1998). References. Verma, V.K., Pande, M.C., 1989, On the association between coronal mass ejections and coronal holes ( Proc. IAU Coll.104 "Solar and Steller Flares", Poster Papers; Stanford Uni, Stanford, USA, p. 239). | |
| Presentor: | Shanil Virani |
| Title: | Monitoring The Chandra X-ray Observatory Radiation Environment: Correlations Between GOES-8, Chandra, and ACE During DOY 89 to DOY 106, 2001 |
| Authors: | Virani, S., N. (Harvard-Smithsonian Center for Astrophysics)
Plucinsky, P., P. (Harvard-Smithsonian Center for Astrophysics) |
| The time period between DOY 89 (March 30) and DOY 106 (April 16), 2001 will likely be remembered as one of the most active time spans in this solar cycle. During this period of activity, the Sun unleashed many M and X-class solar flares. Two of which, an X20 and an X17, were amongst the largest solar flares recorded in the last 10 years. Indeed the sunspot group responsible for this activity, AR 9393, will also likely be recorded as the most active sunspot group of this solar cycle. The Chandra X-ray Observatory, NASA's latest "Great Observatory", was launched on July 23, 1999. The highly elliptical orbit of the CXO (perigee ~ 10,000 km, apogee ~ 140,000 km, 28.5 degree initial inclination) takes the satellite outside of the Earth's magnetosphere during a large fraction of the year. In this location, the CXO is directly exposed to the particles released during solar flares/CMEs, resulting in high background and possible damage to the science instruments. In this poster, we present data from the radiation monitor on-board the CXO, the EPHIN, as well as from the EPAM instrument on-board the ACE satellite (located at L1), and the SEM instrument on-board the GOES-8 satellite (in a geostationary, near-Earth orbit). In particular, we find a very strong correlation between the EPHIN P4 channel and the GOES-8 P2 channel; there is also a correlation between the EPHIN P41 channel and the GOES-8 P5 channel. These correlations allow the Science Operations Team of the CXO to better gauge the radiation environment of the CXO and to take preventive measures, such as suspending science and protecting the science instruments, when necessary. | |
| Presentor: | Harry Warren |
| Title: | Analysis of Preflare Observations by TRACE and Yohkoh |
| Authors: | Warren, H. P. (Harvard-Smithsonian Center for Astrophysics) |
| Despite several decades of observational and theoretical effort, a complete understanding of solar flares remains elusive. It has been especially difficult to understand how the evolution of the magnetic field triggers a flare and drives the release of energy. In this talk I will review TRACE and Yohkoh observations of pre-flare and impulsive
phase dynamics related to nonthermal broadening, flare ribbon evolution, and breakout reconnection. Studies of these phenomena suggest that pre-flare activity is a potentially rich source of information on the mechanisms that power a flare. For example, Yohkoh BCS measurements of nonthermal broadening have shown that the largest nonthermal velocities can occur before the onset of significant hard X-ray emission. This suggests that nonthermal broadening is a signature of a turbulent phase of the flare, which can begin several minutes before the onset of the hard x-ray emission. TRACE observations have also yielded evidence for ribbon brightenings that precede the onset of the hard X-ray emission. The analysis of very high cadence TRACE data, however, indicates that energy release during the pre-flare and impulsive phases of the flare is occurring on different loops. Finally, comparisons of pre-flare TRACE images with potential field extrapolations have shown that pre-flare activity associated with a null point in the field is an essential component of eruptive flares. Understanding the relationships between these phenomena will require coordinated observations between many instruments. I will discuss how future observations from Yohkoh, TRACE, SoHO, HESSI, Stereo, Solar-B, and ground-based observatories will be used to advance our understanding of flare physics. | |
| Presentor: | Mark Weber |
| Title: | Differential Rotation of the Soft X-Ray Corona over a Solar Cycle |
| Authors: | Weber, M.A. (CSSA - Stanford University)
Sturrock, P.A. (CSSA - Stanford University) |
| The Yohkoh Soft X-ray Telescope has provided unprecedented, high spatial and temporal resolution of the solar corona in X-rays for nearly a complete activity cycle. Building upon earlier work, we perform time-series analysis on bins of the full-disk images (SFDs) to describe the differential rotation of the corona over latitude and cycle phase. The bins are formed by integrating over localized regions in heliographic longitude and latitude. We find that the rotation signal in the data comprises a few (usually two) components which are relatively rigid with respect to time and latitude. The relative strength of these components varies over latitude, which may be the reason previous analyses have indicated a ``slightly differential'' rotation profile over latitude. | |
| Presentor: | Meredith Wills-Davey |
| Title: | Intensity Dynamics of an ``EIT Wave'' Observed in TRACE |
| Authors: | Wills-Davey, M.J. (Montana State University) |
| \begin{document}
On 13 June 1998, an ``EIT Wave'' was observed by the TRACE satellite, propagating from a flare outside the TRACE field of view. The absence of the flare allowed for deep exposure observations, something rare with ``EIT Waves.'' To study intensity dynamics , we examine several slices taken along directions of propagation as a function of time. We find the wave is observable as a propagating crest for 400-500 seconds before it dissipates and/or is disrupted by {\it in-situ} magnetic structures. Many of the crests can be modelled by Gaussian curves. Initial results show that the crests do not exhibit a monotonic dissipation, but instead seem to maintain or increase in intensity for hundreds of seconds before dimming and broadening. In addition, velocities determined by measuring from peak intensities (the ``center'' of the wave rather than a visually determined wave front) give initial results of 85-185 km/s, substantially slower than velocities measured for other ``EIT Waves'' (and previously for this event). We use these results to consider and constrain physical mechanisms for ``EIT Waves.'' \end{document} | |
| Presentor: | Henry Winter |
| Title: | Combining SXT and CDS Observations to Investigate Coronal Abundances |
| Authors: | Winter, H.D. (Montana State University Solar Physics Group)
Cirtain, J.W. (Montana State University Solar Physics Group) |
| Coronal elemental abundances vary from their photospheric counterparts, and this variation is known to be related to the first ionization potential (FIP) of the element in question. There are currently three competing empirical models in the literature that broadly describe the abundance of trace elements in the corona. However, it has been shown that elemental abundances are not static across the corona. Abundances vary from region to region and can vary within a coronal structure such as a streamer or loop. In this study the variations of elemental abundances were investigated along a coronal loop structure, near the solar limb, using multi-thermal analysis techniques.
In order to determine elemental abundances, differential emission measure curves were first generated for different points along a coronal loop that was observed by both the Coronal Diagnostic Spectrograph (CDS) aboard the SOHO satellite and by the Soft X-ray Telescope (SXT) aboard Yohkoh. SXT may seem to be an unlikely candidate in the search for abundance values since it is a broadband instrument and not a spectrometer. However, the abundances chosen to calculate the SXT synthetic spectrum have been found to affect the instrument response function, and the SXT's sensitivity to higher temperature provides a much-needed constraint in the calculation of the differential emission measure curves used in this method of analysis. An input model of elemental abundance values was then used to calculate theoretical fluxes for each point along the loop. The theoretical values were then compared to observed data. In order to determine elemental abundance values, the input model was iteratively adjusted until differences between theoretical and observed flux values were minimized. | |
| Presentor: | Kentaro Yaji |
| Title: | Solar Public Observations in Japan |
| Authors: | Yaji, K (Kawabe Cosmic Park) |
| Solar Public Observations in Japan
Kentaro Yaji Kawabe Cosmic ParK Now in Japan, there are more than fifty astronomical educational facilities which have solar telescopes, for example, public observatories and science museums. Because many of the solar telescopes have H-alpha filters, such avtive chromospheric phenomena as solar flares and prominences are easiliy presented to the public. Though main purposes of these solar telescopes must be education and public outreach, they have enough good performance to contribute to solar research. But, the staff in the most of facilities don't know well how to observe the sun and how to understand the solar phenomena. So, we started two attempts in order to support their solar observations. One is the administration of the | |
| Presentor: | Seiji Yashiro |
| Title: | Relation between Thermal and Magnetic Properties of Active Regions as a Probe of Coronal Heating Mechanism |
| Authors: | Yashiro, S. (CSPSW, CUA)
Shibata, K. (Kwasan Observatory, Kyoto University) |
| We study the relation between thermal and magnetic properties of active regions in the corona observed with the Soft X-ray Telescope aboard Yohkoh. We derive the mean temperature and pressure of 64 mature active region using the filter-ratio technique, and examine the relationship of region size with temperature and pressure. We find that the temperature $T$ of active regions increases with increasing region size $L$ as $ T \propto L^{0.28}$, while the pressure $P$ slightly decreases with the region size as $P \propto L^{-0.16}$. We confirm the scaling law $T \propto (P \cdot L)^{1/3}$ for mature active regions found by Rosner et al. We examined the magnetic properties of active regions by analyzing 31 active regions observed with SOHO/MDI, and find the following empirical scaling law between thermal and magnetic properties, \begin{center} $U_{th} \propto \Phi^{1.33}, P \propto B^{0.78}$, \end{center} where $U_{th}$, $\Phi$, and $B$ are total thermal energy content, total magnetic flux, and average magnetic flux density of active regions, respectively. The former is consistent with the results of Golub 1980 et al., but the latter is not. Implications of our findings for coronal heating mechanisms are discussed. | |
| Presentor: | Takaaki Yokoyama |
| Title: | Numerical Simulation of a Flare |
| Authors: | Yokoyama, T. (National Astronomical Observatory of Japan) |
| Magnetohydrodynamic simulation of
a flare including the effect of anisotropic heat conduction, chromospheric evaporation, and radiative cooling based on the magnetic reconnection model is performed. In the simulation model, the coronal magnetic energy is converted to the thermal energy of plasma by magnetic reconnection. This energy is transported to the chromosphere by heat conduction along magnetic field lines and causes increase in temperature and pressure of the chromospheric plasma. The pressure gradient force drives upward motion of the plasma toward the corona. i.e. chromospheric evaporation. This enhances the density of the coronal reconnected flare loops, and such evaporated plasma is considered to be the source of observed soft X-ray emission of a flare. The flare loops filled with the evaporated dense plasma cool down due to the radiative cooling effect. The EUV emitting post-flare loops thus are reproduced in the simulation. | |
| Presentor: | Masato Yoshimori |
| Title: | Intense Gamma-Ray Flare on 6 November, 1997 |
| Authors: | Yoshimori, M. (Rikkyo University
)
Ogawa, H. (Rikkyo University ) Murphy, R.J. (Naval Research Laboratory ) Share, G.H. (Naval Research Laboratory ) |
| A X9.4/3B flare at 11:52 UT on 6 November, 1997 is the most
intense gamma-ray event which Yohkoh has observed so far. Gamma-ray lines resulting from nuclear deexcitation (C line at 4.44 MeV and O line at 6.13 MeV), neutron capture (2.22 MeV) and positron annihilation (0.51 MeV) were measured. Further, high-energy gamma-rays above 10 MeV which are likely due to pion-decay were detected. In adddition to gamma-rays, the Oriented Scintillation Spectrometer Experiment onboard Compton Gamma Ray Observatory recorded flare-associated neutrons after the intense gamma-ray emission was over. The neutron time profile suggests the possibility of extended particle acceleration. We discuss characteristics of high-energy particles at the flare site based on the available data of gamma-rays, neutrons and X-ray images and compare them with those of CME-associated solar energetic particles. | |
| Presentor: | Keiji YOSHIMURA |
| Title: | Surges, magnetic flux cancellations and UV brightenings around an emerging flux region. |
| Authors: | Yoshimura, K (The Institute of Space and Astronautical Science, Japan)
Kurokawa, H (Kwasan Observatory, Kyoto Univ., Japan) Shimojo, M (Nobeyama Radio Observatory, NAOJ, Japan) Shine, R (Lockheed Martin Solar and Astrophysics Laboratory, US) |
| Surge activities, which are observed in H$alpha$ images, have been
studying for a long time. Many authors noticed that cancellations of magnetic flux was an important factor for surge activities and proposed the models based on magnetic reconnection. But there are not many observations which have enough cadence for comparison changes of magnetic field with surge activities. So the correlation between surges and magnetic flux cancellations is not clear yet. (ex. Zhang et al. 2001) We studied the temporal and spatial relations between surge activities and other phenomena which may be accompanied by surge activities. The data we used here are from coordinated observation with Swedish Vacuum Solar Telescope on La Palma, TRACE and SOHO/MDI. So high cadence images for the same target are available in various wavelengths. MDI, for example, took magnetogram data every one minutes with high resolution mode at that time. The main results from this study are as follows: (1) We can not find any large time lag between the onset of the surge and of the magnetic fields cancellation. This is a conflict result against the one in Zhang et al. (2) There were UV brightenings which correlated well with rapid cancellation of magnetic fields. (3) The UV brightenings located just on neutral lines with some displacement from the region where rapid magnetic cancellation occurred. These observational fact can be explained by magnetic reconnection model. | |