Multi-Wavelength Observations of Coronal Structure and Dynamics -- Yohkoh 10th Anniversary Meeting

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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 principlef, 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 NASA’s 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 SECEF’s 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 NASA’s 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 Narukag