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Kinematical properties of coronal mass ejections  

Manuela Temmer   Submitted: 2016-03-07 01:29

Coronal mass ejections (CMEs) are the most dynamic phenomena in our solar system. They abruptly disrupt the continuous outflow of solar wind by expelling huge clouds of magnetized plasma into interplanetary space with velocities enabling to cross the Sun-Earth distance within a few days. Earth-directed CMEs may cause severe geomagnetic storms when their embedded magnetic fields and the shocks ahead compress and reconnect with the Earth's magnetic field. The transit times and impacts in detail depend on the initial CME velocity, size, and mass, as well as on the conditions and coupling processes with the ambient solar wind flow in interplanetary space. The observed CME parameters may be severly affected by projection effects and the constant changing environmental conditions are hard to derive. This makes it difficult to fully understand the physics behind CME evolution, preventing to do a reliable forecast of Earth-directed events. This short review focusing on observational data, shows recent methods which were developed to derive the CME kinematical profile for the entire Sun-Earth distance range as well as studies which were performed to shed light on the physical processes that CMEs encounter when propagating from Sun to Earth.

Authors: M. Temmer
Projects: SoHO-EIT,SoHO-LASCO,STEREO

Publication Status: accepted for publication in Astronomische Nachrichten
Last Modified: 2016-03-08 12:17
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Thermosphere and geomagnetic response to interplanetary coronal mass ejections observed by ACE and GRACE: Statistical results  

Manuela Temmer   Submitted: 2015-10-14 01:04

For the period July 2003 to August 2010, the interplanetary coronal mass ejection (ICME) catalogue maintained by Richardson and Cane lists 106 Earth-directed events, which have been measured in-situ by plasma and field instruments onboard the ACE satellite. We present a statistical investigation of the Earth's thermospheric neutral density response by means of accelerometer measurements collected by the GRACE satellites, which are available for 104 ICMEs in the data set, and its relation to various geomagnetic indices and characteristic ICME parameters such as the impact speed, southward magnetic field strength (Bz). The majority of ICMEs causes a distinct density enhancement in the thermosphere, with up to a factor of eight compared to the pre-event level. We find high correlations between ICME Bz and thermospheric density enhancements (~0.9), while the correlation with the ICME impact speed is somewhat smaller (~0.7). The geomagnetic indices revealing the highest correlations are Dst and SYM-H (~0.9), the lowest correlations are obtained for kp and AE (~0.7), which show a nonlinear relation with the thermospheric density enhancements. Separating the response for the shock sheath region and the magnetic structure of the ICME, we find that the Dst and SYM-H reveal a tighter relation to the Bz minimum in the magnetic structure of the ICME, whereas the polar cap indices show higher correlations with the Bz minimum in the shock sheath region. Since the strength of the Bz component - either in the sheath or the magnetic structure of the ICME - is highly correlated (~0.9) with the neutral density enhancement, we discuss the possibility of satellite orbital decay estimates based on magnetic field measurements at L1, i.e. before the ICME hits the Earth's magnetosphere. This will further stimulate progress in space weather understanding and applications regarding satellite operations.

Authors: S. Krauss, M. Temmer, A.M. Veronig, O. Baur, H. Lammer
Projects: ACE

Publication Status: published in JGR; DOI: 10.1002/2015JA021702
Last Modified: 2015-10-15 07:27
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Interplanetary Propagation Behavior of the Fast Coronal Mass Ejection from 23 July 2012  

Manuela Temmer   Submitted: 2014-11-25 00:14

The fast coronal mass ejection (CME) from 23 July 2012 raised attention due to its extremely short transit time from Sun to 1 AU of less than 21 h. In-situ data from STEREO-A revealed the arrival of a fast forward shock with a speed of more than 2200 km s-1 followed by a magnetic structure moving with almost 1900 km s-1. We investigate the propagation behavior of the CME shock and magnetic structure with the aim to reproduce the short transit time and high impact speed as derived from in-situ data. We carefully measure the 3D kinematics of the CME using the graduated cylindrical shell model, and obtain a maximum speed of 2580"280 km s-1 for the CME shock and of 2270"420 km s-1 for its magnetic structure. Based on the 3D kinematics, the drag-based model (DBM) reproduces the observational data reasonably well. To successfully simulate the CME shock, we find that the ambient flow speed should be of average value close to the slow solar wind speed (450 km s-1), and the initial shock speed at a distance of 30 Rs should not exceed ≈2300 km s-1, otherwise it would arrive much too early at STEREO-A. The model results indicate that an extremely low aerodynamic drag force is exerted on the shock, smaller by one order of magnitude compared to the average. As a consequence, the CME hardly decelerates in interplanetary space and maintains its high initial speed. The low aerodynamic drag can only be reproduced when reducing the density of the ambient solar wind flow, in which the massive CME propagates, to rho_sw=1-2 cm-3 at the distance of 1 AU. This result is consistent with the preconditioning of interplanetary space owing to a previous CME.

Authors: Manuela Temmer and Nariaki Nitta
Projects: SDO-AIA,SoHO-LASCO,STEREO

Publication Status: in press for Solar Physics
Last Modified: 2014-11-25 08:18
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Asymmetry in the CME-CME interaction process for the events from 2011 February 14-15  

Manuela Temmer   Submitted: 2014-02-28 01:23

We present a detailed study of the interaction process of two coronalmass ejections (CMEs) successively launched on 2011 February 14 (CME1)and 2011 February 15 (CME2). Reconstructing the 3D shape and evolutionof the flux ropes we verify that the two CMEs interact. The frontalstructure of both CMEs measured along different position angles (PA)over the entire latitudinal extent, reveals differences in thekinematics for the interacting flanks and the apexes. The interactionprocess is strongly PA-dependent in terms of timing as well askinematical evolution. The central interaction occurs along PA-100°,which shows the strongest changes in kinematics. During interaction,CME1 accelerates from ~400 km s-1 to ~700 km s-1 and CME2 decelerates from~1300 km s-1 to ~600 km s-1. Our results indicate that a simplifiedscenario like inelastic collision may not be sufficient to describethe CME-CME interaction. Magnetic field structures of the intertwiningflux ropes as well as momentum transfer due to shocks play animportant role in the interaction process.

Authors: M. Temmer, A. M. Veronig, V. Peinhart, B. Vrsnak
Projects: PROBA2/SWAP,SoHO-LASCO,STEREO

Publication Status: ApJ (accepted)
Last Modified: 2014-03-04 16:08
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The Wave-Driver System of the Off-Disk Coronal Wave 17 January 2010  

Manuela Temmer   Submitted: 2012-07-13 00:08

We study the 17 January 2010 flare-CME-wave event by using STEREO/SECCHI EUVI and COR1 data. The observational study is combined with an analytic model which simulates the evolution of the coronal-wave phenomenon associated with the event. From EUV observations, the wave signature appears to be dome shaped having a component propagating on the solar surface (v~280 km s-1) as well as off-disk (v~600 km s-1) away from the Sun. The off-disk dome of the wave consists of two enhancements in intensity, which conjointly develop and can be followed up to white-light coronagraph images. Applying an analytic model, we derive that these intensity variations belong to a wave-driver system with a weakly shocked wave, initially driven by expanding loops, which are indicative of the early evolution phase of the accompanying CME. We obtain the shock standoff distance between wave and driver from observations as well as from model results. The shock standoff distance close to the Sun (<0.3 Rs above the solar surface) is found to rapidly increase with values of ~0.03-0.09 Rs which give evidence of an initial lateral (over-)expansion of the CME. The kinematical evolution of the on-disk wave could be modeled using input parameters which require a more impulsive driver (t=90 s, a=1.7 km s-2) compared to the off-disk component (t=340 s, a=1.5 km s-2).

Authors: M. Temmer, B. Vrsnak, A. M. Veronig
Projects: STEREO

Publication Status: accepted for publication in Solar Physics
Last Modified: 2012-07-13 10:38
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Characteristics of kinematics of a coronal mass ejection during the 2010 August 1 CME-CME interaction event  

Manuela Temmer   Submitted: 2012-02-09 00:31

We study the interaction of two successive coronal mass ejections (CMEs)during the 2010 August 1 events using STEREO/SECCHI COR and HI data. We obtainthe direction of motion for both CMEs by applying several independentreconstruction methods and find that the CMEs head in similar directions. Thisprovides evidence that a full interaction takes place between the two CMEs thatcan be observed in the HI1 field-of-view. The full de-projected kinematics ofthe faster CME from Sun to Earth is derived by combining remote observationswith in situ measurements of the CME at 1 AU. The speed profile of the fasterCME (CME2; ~1200 km s-1) shows a strong deceleration over the distance range atwhich it reaches the slower, preceding CME (CME1; ~700 km s-1). By applying adrag-based model we are able to reproduce the kinematical profile of CME2suggesting that CME1 represents a magnetohydrodynamic obstacle for CME2 andthat, after the interaction, the merged entity propagates as a single structurein an ambient flow of speed and density typical for quiet solar windconditions. Observational facts show that magnetic forces may contribute to theenhanced deceleration of CME2. We speculate that the increase in magnetictension and pressure, when CME2 bends and compresses the magnetic field linesof CME1, increases the efficiency of drag.

Authors: Temmer, M.; Vrsnak, B.; Rollett, T.; Bein, B.; de Koning, C.A.; Liu, Y.; Bosman, E.; Davies, J.A.; Möstl, C.; Zic, T.; Veronig, A.M.; Bothmer, V.; Harrison, R.; Nitta, N.; Bisi, M.; Flor, O.; Eastwood, J.; Odstrcil, D.; Forsyth, R.
Projects: STEREO

Publication Status: ApJ (in press)
Last Modified: 2012-02-09 11:25
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Influence of the ambient solar wind flow on the propagation behavior of interplanetary CMEs  

Manuela Temmer   Submitted: 2011-10-06 00:07

We study three CME/ICME events (2008 June 1-6, 2009 February 13-18, 2010April 3-5) tracked from Sun to 1 AU in remote-sensing observations of STEREOHeliospheric Imagers and in situ plasma and magnetic field measurements. Wefocus on the ICME propagation in IP space that is governed by two forces, thepropelling Lorentz force and the drag force. We address the question at whichheliospheric distance range the drag becomes dominant and the CME gets adjustedto the solar wind flow. To this aim we analyze speed differences between ICMEsand the ambient solar wind flow as function of distance. The evolution of theambient solar wind flow is derived from ENLIL 3D MHD model runs using differentsolar wind models, namely Wang-Sheeley-Arge (WSA) and MHD-Around-A-Sphere(MAS). Comparing the measured CME kinematics with the solar wind models we findthat the CME speed gets adjusted to the solar wind speed at very differentheliospheric distances in the three events under study: from below 30 Rs, tobeyond 1 AU, depending on the CME and ambient solar wind characteristics. ENLILcan be used to derive important information about the overall structure of thebackground solar wind, providing more reliable results during times of lowsolar activity than during times of high solar activity. The results from thisstudy enable us to get a better insight into the forces acting on CMEs over theIP space distance range, which is an important prerequisite in order to predicttheir 1 AU transit times.

Authors: Temmer, M., Rollett, T., Möstl, C., Veronig, A.M., Vrsnak, B.
Projects: STEREO

Publication Status: ApJ (in press)
Last Modified: 2011-10-06 11:40
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Relation between the 3D-geometry of the coronal wave and associated CME during the 26 April 2008 event  

Manuela Temmer   Submitted: 2011-03-02 00:14

We study the kinematical characteristics and 3D geometry of alarge-scale coronal wave that occurred in association with the 26April 2008 flare-CME event. The wave was observed with the EUVIinstruments aboard both STEREO spacecraft (STEREO-A and STEREO-B) witha mean speed of ~240 km s-1. The wave is more pronounced in the easternpropagation direction, and is thus, better observable in STEREO-Bimages. From STEREO-B observations we derive two separate initiationcenters for the wave, and their locations fit with the coronal dimmingregions. Assuming a simple geometry of the wave we reconstruct its 3Dnature from combined STEREO-A and STEREO-B observations. We find thatthe wave structure is asymmetric with an inclination towards East. Theassociated CME has a deprojected speed of ~750±50 km s-1, and shows anon-radial outward motion towards the East with respect to theunderlying source region location. Applying the forward fitting modeldeveloped by Thernisien, Howard, and Vourlidas (2006), we derive theCME flux rope position on the solar surface to be close to the dimmingregions. We conclude that the expanding flanks of the CME most likelydrive and shape the coronal wave.

Authors: M. Temmer, A.M. Veronig, N. Gopalswamy, S. Yashiro
Projects: STEREO

Publication Status: Solar Physics (in press)
Last Modified: 2011-03-02 08:59
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Combined STEREO/RHESSI study of CME acceleration and particle acceleration in solar flares  

Manuela Temmer   Submitted: 2010-02-16 06:24

Using the potential of two unprecedented missions, STEREO and RHESSI, we study three well observed fast CMEs that occurred close to the limb together with their associated high energy flare emissions in terms of RHESSI HXR spectra and flux evolution. From STEREO/EUVI and STEREO/COR1 data the full CME kinematics of the impulsive acceleration phase up to 4 Rs is measured with a high time cadence of less equal 2.5 min. For deriving CME velocity and acceleration we apply and test a new algorithm based on regularization methods. The CME maximum acceleration is achieved at heights h < 0.4 Rs, the peak velocity at h < 2.1 Rs (in one case as small as 0.5 Rs). We find that the CME acceleration profile and the flare energy release as evidenced in the RHESSI hard X-ray flux evolve in a synchronized manner. These results support the standard flare/CME model which is characterized by a feed-back relationship between the large-scale CME acceleration process and the energy release in the associated flare.

Authors: M. Temmer, A.M. Veronig, E.P. Kontar, S. Krucker, B. Vrsnak
Projects: RHESSI,STEREO

Publication Status: ApJ (accepted)
Last Modified: 2010-02-16 10:18
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Analytic modeling of the Moreton wave kinematics  

Manuela Temmer   Submitted: 2009-08-26 01:49

The issue whether Moreton waves are flare-ignited or CME-driven, or a combination of both, is still a matter of debate. We develop an analytical model describing the evolution of a large-amplitude coronal wave emitted by the expansion of a circular source surface in order to mimic the evolution of a Moreton wave. The model results are confronted with observations of a strong Moreton wave observed in association with the X3.8/3B flare/CME event from January 17, 2005. Using different input parameters for the expansion of the source region, either derived from the real CME observations (assuming that the upward moving CME drives the wave), or synthetically generated scenarios (expanding flare region, lateral expansion of the CME flanks), we calculate the kinematics of the associated Moreton wave signature. Those model input parameters are determined which fit the observed Moreton wave kinematics best. Using the measured kinematics of the upward moving CME as the model input, we are not able to reproduce the observed Moreton wave kinematics. The observations of the Moreton wave can be reproduced only by applying a strong and impulsive acceleration for the source region expansion acting in a piston mechanism scenario. Based on these results we propose that the expansion of the flaring region or the lateral expansion of the CME flanks is more likely the driver of the Moreton wave than the upward moving CME front.

Authors: Temmer, M., Vrsnak, B., Zic, T., Veronig, A.M.
Projects: RHESSI,SoHO-MDI,SoHO-LASCO

Publication Status: ApJ, 2009, 702, p.1343
Last Modified: 2009-08-26 09:20
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STEREO quadrature observations of the 3D structure and driver of a global coronal wave  

Manuela Temmer   Submitted: 2009-08-25 03:46

We present the first observations of a global coronal wave (''EIT wave'') from the two Solar Terrestrial Relations Observatory (STEREO) satellites in quadrature. The wave's initiation site was at the disk center in STEREO-B and precisely on the limb in STEREO-A. These unprecedented observations from the STEREO Extreme Ultraviolet Imaging (EUVI) instruments enable us to gain insight into the wave's kinematics, initiation and 3D structure. The wave propagates globally over the whole solar hemisphere visible to STEREO-B with a constant velocity of 263±16 km s-1. From the two STEREO observations we derive a height of the wave in the range of 80-100 Mm. Comparison of the wave kinematics with the early phase of the erupting CME structure indicates that the wave is initiated by the CME lateral expansion, and then propagates freely with a velocity close to the fast magnetosonic speed in the quiet solar corona.

Authors: Kienreich, I.W., Temmer, M., and Veronig, A.M.
Projects: STEREO

Publication Status: ApJ Letters (accepted)
Last Modified: 2009-08-25 09:00
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CME projection effects studied with STEREO/COR and SOHO/LASCO  

Manuela Temmer   Submitted: 2009-04-10 00:46

Based on a set of eleven CME events we study the impact of projection effects by tracking CME leading edge features in the plane-of-sky (traditional CME tracking) from combined STEREO/SECCHI-SOHO/LASCO observations up to 20Rs. Using CME observations from two vantage points and applying triangulation techniques, the source region location of the CME on the solar surface was determined (heliospheric longitude and latitude) in order to correct for projection effects. With this information, the directivity and 'true' speed of a CME can be estimated in a simple way. The comparison of the results obtained from the spacecraft pairs SOHO-LASCO/STEREO-A and SOHO-LASCO/STEREO-B allows us to study the reliability of the method. The determined CME source region is generally coincident within less than 10 degrees.

Authors: Temmer, M., Preiss, S., Veronig, A. M.
Projects: SoHO-LASCO,STEREO

Publication Status: Solar Physics (in press)
Last Modified: 2009-04-10 08:24
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Subject will be restored when possible  

Manuela Temmer   Submitted: 2008-06-05 01:22

We report a large-scale coronal wave (so-called 'EIT wave') observed with high cadence by EUVI onboard STEREO in association with the GOES B9.5 flare and double CME event on 19 May 2007. The EUVI instruments provide us with the unprecedented opportunity to study the dynamics of flare/CME associated coronal waves. The coronal wave under study reveals deceleration, indicative of a freely propagating MHD wave. Complementary analysis of the associated flare and erupting filament/CME hint at wave initiation by the CME expanding flanks, which drive the wave only over a limited distance. The associated flare is very weak and occurs too late to account for the wave initiation.

Authors: Veronig, A.M., Temmer, M., Vrsnak, B.
Projects: STEREO

Publication Status: ApJ Letters (accepted)
Last Modified: 2008-09-23 21:00
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Subject will be restored when possible  

Manuela Temmer   Submitted: 2007-12-06 04:29

We study two well observed, fast halo CMEs, covering the full CME kinematics including the initiation and impulsive acceleration phase, and their associated flares. We find a close synchronization between the CME acceleration profile and the flare energy release as indicated by the RHESSI hard X-ray flux - onsets as well as peaks occur simultaneously within 5~min. These findings indicate a close physical connection between both phenomena, and are interpreted in terms of a feed-back relationship between the CME dynamics and the reconnection process in the current sheet beneath the CME.

Authors: Temmer, M., Veronig, A.M., Vrsnak, B., Ryb?k, J., G?m?ry, P., Stoiser, S., Maricic, D.
Projects: RHESSI,SoHO-EIT,SoHO-LASCO,TRACE

Publication Status: ApJ Letters (accepted)
Last Modified: 2007-12-06 07:45
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Subject will be restored when possible  

Manuela Temmer   Submitted: 2007-12-06 04:29

We study two well observed, fast halo CMEs, covering the full CME kinematics including the initiation and impulsive acceleration phase, and their associated flares. We find a close synchronization between the CME acceleration profile and the flare energy release as indicated by the RHESSI hard X-ray flux - onsets as well as peaks occur simultaneously within 5~min. These findings indicate a close physical connection between both phenomena, and are interpreted in terms of a feed-back relationship between the CME dynamics and the reconnection process in the current sheet beneath the CME.

Authors: Temmer, M., Veronig, A.M., Vrsnak, B., Rybak, J., Gömöry, P., Stoiser, S., Maricic, D.
Projects: RHESSI,SoHO-EIT,SoHO-LASCO,TRACE

Publication Status: ApJ Letters (accepted)
Last Modified: 2007-12-06 08:44
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Subject will be restored when possible  

Manuela Temmer   Submitted: 2007-12-06 04:29

We study two well observed, fast halo CMEs, covering the full CME kinematics including the initiation and impulsive acceleration phase, and their associated flares. We find a close synchronization between the CME acceleration profile and the flare energy release as indicated by the RHESSI hard X-ray flux - onsets as well as peaks occur simultaneously within 5~min. These findings indicate a close physical connection between both phenomena, and are interpreted in terms of a feed-back relationship between the CME dynamics and the reconnection process in the current sheet beneath the CME.

Authors: Temmer, M., Veronig, A.M., Vrsnak, B., Rybak, J., Gömöry, P., Stoiser, S., Maricic, D.
Projects: RHESSI,SoHO-EIT,SoHO-LASCO,TRACE

Publication Status: ApJ Letters (accepted)
Last Modified: 2007-12-07 01:26
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Energy release rates of H α flare ribbons and locations of HXR sources  

Manuela Temmer   Submitted: 2006-09-19 23:19

Local reconnection and energy release rates for an X3.8 flare that occurred on 17 January, 2005 are derived. In particular, we distinguished between H α flare ribbon segments that were accompanied by RHESSI hard X-ray (HXR) footpoints and those without HXRs. We find that the reconnection and energy release rates are not uniform along the flare ribbons but much larger at the locations where the HXR footpoints are observed. The difference is about two orders of magnitude in case of the energy release rates and one order of magnitude for the reconnection rates (with peak values up to 8 kV/m). These differences are enough to explain the different flare morphologies typically observed in HXRs (compact footpoints) and H α /UV (extended ribbons) by the limited dynamic range of present HXR instruments. Our results are consistent with a scenario where the electrons are accelerated primarily along a certain subsystem of magnetic loops as outlined by the hard X-ray footpoints, and only a minor fraction (for the 17 January, 2005 flare estimated to about 1/15) goes into the large flare arcade outlined by the H α ribbons and EUV postflare loops.

Authors: Temmer, M., Veronig, A., Vrsnak, B., Miklenic, C.
Projects: RHESSI

Publication Status: ApJ (accepted)
Last Modified: 2006-09-21 10:46
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SHRINKING AND COOLING OF FLARE LOOPS IN A TWO-RIBBON FLARE  

Manuela Temmer   Submitted: 2005-12-19 02:38

We analyze the evolution of the flare/postflare loop system in the two-ribbon flare of 3 November 2003, utilizing multi-wavelength observations that cover the temperature range from several tens MK down to 104 K. A non-uniform growth of the loop system enables us to identify analogous patterns in the height-time, h(t), curves measured at different temperatures. The “knees”, “plateaus”, and “bends” in a higher-temperature curve appear after a certain time delay at lower heights in a lower-temperature curve. We interpret such a shifted replication as a track of a given set of loops (reconnected field lines) while shrinking and cooling after being released from the reconnection site. Measurements of the height/time shifts between h(t) curves of different temperatures provide a simultaneous estimate of the shrinkage speed and cooling rate in a given temperature domain, for a period of almost ten hours after the flare impulsive phase. From the analysis we find: a) Loop shrinkage is faster at higher temperatures – in the first hour of the loop system growth the shrinkage velocity at 5 MK is 20–30 km s-1, whereas at 1 MK it amounts to 5 km s-1; b) Shrinking becomes slower as the flare decays – ten hours after the impulsive phase the shrinkage velocity at 5 MK becomes 5 km s-1; c) The cooling rate decreases as the flare decays – in the 5 MK range it is 1 MK/min in the first hour of the loop system growth, whereas ten hours later it decreases to 0.2 MK/min; d) During the initial phase of the loop system growth the cooling rate is larger at higher temperatures, whereas in the late phases the cooling rate apparently does not depend on the temperature; e) A more detailed analysis of shrinking/cooling around 1 hour after the impulsive phase reveals a deceleration of the loop shrinkage, amounting to a~10m s-2 in theT < 5 MK range; f) In the same interval the conductive cooling dominates down to T~3 MK, whereas radiation becomes dominant below T~2 MK; g) A few hours after the impulsive phase the radiation becomes dominant across the whole T < 5 MK range. These findings are compared with results of previous studies and discussed in the framework of relevant models.

Authors: Vrsnak, B., Veronig, A., Temmer, M., Karlicky, M., Lin, J.
Projects: RHESSI,Soho-EIT

Publication Status: Solar Physics (accepted)
Last Modified: 2005-12-19 02:40
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Does solar flare activity lag behind sunspot activity?  

Manuela Temmer   Submitted: 2003-05-26 03:11

Recently, Wheatland & Litvinenko (2001) have suggested that over the solar cycle both the flaring rate and the magnetic free energy in the corona lag behind the energy supply to the system. To test this model result, we analyzed the evolution of solar flare occurrence with regard to Sunspot Numbers (as well as sunspot areas), using H α flare data available for the period 1955-2002, and soft X-ray flare data (GOES 1-8 Angstroem) for the period 1976-2002. For solar cycles 19, 21 and 23, we find a characteristic time lag between flare activity and sunspot activity in the range ~10 < tau < ~15 months, consistent with the model predictions by Wheatland & Litvinenko (2001). The phenomenon turns out to be more prominent for high-energetic flares. The investigation of solar activity separately for the northern and southern hemisphere, allows us to exclude any bias due to overlapping effects from the activity of both hemispheres and confirms the dynamic relevance of the delay phenomenon. Yet, no characteristic time lag tau > 0 is found for solar cycles 20 and 22. The finding that in odd-numbered cycles flare activity is statistically delayed with respect to sunspot activity, while in even-numbered cycles it is not, suggests a connection to the 22-year magnetic cycle of the Sun. Further insight into the connection to the 22-year magnetic cycle could possibly be gained when a 22-year variation in the energy supply rate is taken into account in the Wheatland & Litvinenko (2001) model. The existence of a 22-year modulation in the energy supply rate is suggested by the empirical Gnevyshev-Ohl rule, and might be caused by a relic solar field.

Authors: Temmer, M., Veronig, A. and Hanslmeier, A.
Projects: None

Publication Status: Solar Physics (in press)
Last Modified: 2003-05-26 03:11
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Statistical analysis of solar H α flares  

Manuela Temmer   Submitted: 2002-10-02 09:35

A statistical analysis of a large data set of H α flares comprising almost 100 000 single events that occurred during the period January 1975 to December 1999 is presented. We analyzed the flares evolution steps, i.e. duration, rise times, decay times and event asymmetries. Moreover, these parameters characterizing the temporal behavior of flares, as well as the spatial distribution on the solar disk, i.e. N-S and E-W asymmetries, are analyzed in terms of their dependency on the solar cycle. The main results are: 1) The duration, rise and decay times increase with increasing importance class. The increase is more pronounced for the decay times than for the rise times. The same relation is valid with regard to the brightness classes but in a weaker manner. 2) The event asymmetry indices, which characterize the proportion of the decay to the rise time of an event, are predominantly positive (ca. 90%). For about 50% of the events the decay time is even more than 4 times as long as the rise time. 3) The event asymmetries increase with the importance class. 4) The flare duration and decay times vary in phase with the solar cycle; the rise times do not. 5) The event asymmetries do not reveal a distinct correlation with the solar cycle. However, they drop during times of solar minima, which can be explained by the shorter decay times found during minimum activity. 6) There exists a significant N-S asymmetry over longer periods, and the dominance of one hemisphere over the other can persist for more than one cycle. 7) For certain cycles there may be evidence that the N-S asymmetry evolves with the solar cycle, but in general this is not the case. 8) There exists a slight but significant E-W asymmetry with a prolonged eastern excess.

Authors: M. Temmer, A. Veronig, A. Hanslmeier, W. Otruba, and M. Messerotti
Projects:

Publication Status: A&A 375, 2001, 1049–1061
Last Modified: 2002-10-02 09:35
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Abstracts by Author
Kinematical properties of coronal mass ejections
Thermosphere and geomagnetic response to interplanetary coronal mass ejections observed by ACE and GRACE: Statistical results
Interplanetary Propagation Behavior of the Fast Coronal Mass Ejection from 23 July 2012
Asymmetry in the CME-CME interaction process for the events from 2011 February 14-15
The Wave-Driver System of the Off-Disk Coronal Wave 17 January 2010
Characteristics of kinematics of a coronal mass ejection during the 2010 August 1 CME-CME interaction event
Influence of the ambient solar wind flow on the propagation behavior of interplanetary CMEs
Relation between the 3D-geometry of the coronal wave and associated CME during the 26 April 2008 event
Combined STEREO/RHESSI study of CME acceleration and particle acceleration in solar flares
Analytic modeling of the Moreton wave kinematics
STEREO quadrature observations of the 3D structure and driver of a global coronal wave
CME projection effects studied with STEREO/COR and SOHO/LASCO
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Subject will be restored when possible
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Subject will be restored when possible
Energy release rates of H-alpha flare ribbons and locations of HXR sources
SHRINKING AND COOLING OF FLARE LOOPS IN A TWO-RIBBON FLARE
Does solar flare activity lag behind sunspot activity?
Statistical analysis of solar H-alpha flares

Related Pages
MSU Solar Physics.
Max Millennium Science Mail Archive.
Max Millennium Message of the Day Mail Archive.
Max Millennium Flare Catalog

Archive Maintainer
Alisdair Davey



© 2003 Solar Physics Group - Montana State University