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A Tiny Eruptive Filament as a Flux-Rope Progenitor and Driver of a Large-Scale CME and Wave  

Victor Grechnev   Submitted: 2016-04-04 21:36

A solar eruptive event SOL2010-06-13 observed with the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO) has been extensively discussed in the contexts of the CME development and an associated extreme-ultraviolet (EUV) wave-like transient in terms of a shock driven by the apparent CME rim. Continuing the analysis of this event, we have revealed an erupting flux rope, studied its properties, and detected wave signatures inside the developing CME. These findings have allowed us to establish new features in the genesis of the CME and associated EUV wave and to reconcile all of the episodes into a single causally-related sequence. (1) A hot 11 MK flux rope developed from the structures initially associated with a compact filament system. The flux rope expanded with an acceleration of up to 3 km s-2 one minute before a hard X-ray burst and earlier than any other structures, reached a velocity of 420 km s-1, and then decelerated to about 50 km s-1. (2) The CME development was driven by the expanding flux rope. Closed coronal structures above the rope got sequentially involved in the expansion from below upwards, came closer together, and apparently disappeared to reveal their common envelope, the visible rim, which became the outer boundary of the cavity. The rim was probably associated with the separatrix surface of a magnetic domain, which contained the pre-eruptive filament. (3) The rim formation was associated with a successive compression of the upper active-region structures into the CME frontal structure (FS). When the rim was formed, it resembled a piston. (4) The disturbance responsible for the consecutive CME formation episodes was excited by the flux rope inside the rim, and then propagated outward. EUV structures arranged at different heights started to accelerate, when their trajectories in the distance-time diagram were crossed by that of the fast front of this disturbance. (5) Outside the rim and FS, the disturbance propagated like a blast wave, manifesting in a type II radio burst and a leading part of the EUV transient. Its main, trailing part was the FS, which consisted of swept-up 2 MK coronal loops enveloping the expanding rim. The wave decelerated and decayed into a weak disturbance soon afterwards, being not driven by the trailing piston, which slowed down.

Authors: V.V. Grechnev, A.M. Uralov, A.A. Kochanov, I.V. Kuzmenko, D.V. Prosovetsky, Ya.I. Egorov, V.G. Fainshtein, L.K. Kashapova
Projects: None,GOES X-rays ,SDO-AIA,SDO-HMI,SoHO-LASCO,STEREO

Publication Status: Accepted for publication in Solar Physics. DOI: 10.1007/s11207-016-0888-z
Last Modified: 2016-04-06 08:20
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Relations between Microwave Bursts and near-Earth High-Energy Proton Enhancements and their Origin  

Victor Grechnev   Submitted: 2015-11-19 00:05

We further study the relations between parameters of bursts at 35 GHz recorded with the Nobeyama Radio Polarimeters during 25 years, on the one hand, and solar proton events, on the other hand (Grechnev et al. in Publ. Astron. Soc. Japan 65, S4, 2013a). Here we address the relations between the microwave fluences at 35 GHz and near-Earth proton fluences above 100 MeV in order to find information on their sources and evaluate their diagnostic potential. A correlation was found to be pronouncedly higher between the microwave and proton fluences than between their peak fluxes. This fact probably reflects a dependence of the total number of protons on the duration of the acceleration process. In events with strong flares, the correlation coefficients of high-energy proton fluences with microwave and soft X-ray fluences are higher than those with the speeds of coronal mass ejections. The results indicate a statistically larger contribution of flare processes to high-energy proton fluxes. Acceleration by shock waves seems to be less important at high energies in events associated with strong flares, although its contribution is probable and possibly prevails in weaker events. The probability of a detectable proton enhancement was found to directly depend on the peak flux, duration, and fluence of the 35 GHz burst, while the role of the Big Flare Syndrome might be overestimated previously. Empirical diagnostic relations are proposed.

Authors: Grechnev, V. V., Kiselev, V. I., Meshalkina, N. S., Chertok, I. M.
Projects: GOES Particles,GOES X-rays ,Other,SoHO-LASCO

Publication Status: Solar Physics, submitted
Last Modified: 2015-11-20 15:39
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Responsibility of a Filament Eruption for the Initiation of a Flare, CME, and Blast Wave, and its Possible Transformation into a Bow Shock  

Victor Grechnev   Submitted: 2014-11-06 23:35

Multi-instrument observations of two filament eruptions on 24 February and 11 May 2011 suggest the following updated scenario for eruptive flare, CME and shock wave evolution. An initial destabilization of a filament results in stretching out of magnetic threads belonging to its body and rooted in the photosphere along the inversion line. Their reconnection leads to i) heating of parts of the filament or its environment, ii) initial development of the flare arcade cusp and ribbons, and iii) increasing similarity of the filament to a curved flux rope and its acceleration. Then the pre-eruption arcade enveloping the filament gets involved in reconnection according to the standard model and continues to form the flare arcade and ribbons. The poloidal magnetic flux in the curved rope developing from the filament progressively increases and forces its toroidal expansion. This flux rope impulsively expands and produces an MHD disturbance, which rapidly steepens into a shock. The shock passes through the arcade expanding above the filament and then freely propagates ahead of the CME like a decelerating blast wave for some time. If the CME is slow, then the shock eventually decays. Otherwise, the frontal part of the shock changes into the bow-shock regime. This was observed for the first time in the 24 February 2011 event. When reconnection ceases, the flux rope relaxes and constitutes the CME core-cavity system. The expanding arcade develops into the CME frontal structure. We also found that reconnection in the current sheet of a remote streamer forced by the shock's passage results in a running flare-like process within the streamer responsible for a type II burst. The development of dimming and various associated phenomena are discussed.

Authors: V. V. Grechnev, A. M. Uralov, I. V. Kuzmenko, A. A. Kochanov, I. M. Chertok, S. S. Kalashnikov
Projects: GOES X-rays ,Other,RHESSI,SDO-AIA,SoHO-LASCO,STEREO

Publication Status: Solar Phys., accepted
Last Modified: 2014-11-07 10:20
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A Challenging Solar Eruptive Event of 18 November 2003 and the Causes of the 20 November Geomagnetic Superstorm. IV. Unusual Magnetic Cloud and Overall Scenario  

Victor Grechnev   Submitted: 2014-09-02 00:06

The geomagnetic superstorm of 20 November 2003 with Dst = -422 nT, one of the most intense in history, is not well understood. The superstorm was caused by a moderate solar eruptive event on 18 November, comprehensively studied in our preceding Papers I-III. The analysis has shown a number of unusual and extremely complex features, which presumably led to the formation of an isolated right-handed magnetic-field configuration. Here we analyze the interplanetary disturbance responsible for the 20 November superstorm, compare some of its properties with the extreme 28-29 October event, and reveal a compact size of the magnetic cloud (MC) and its disconnection from the Sun. Most likely, the MC had a spheromak configuration and expanded in a narrow angle of < 14 degree. A very strong magnetic field in the MC up to 56 nT was due to the unusually weak expansion of the disconnected spheromak in an enhanced-density environment constituted by the tails of the preceding ICMEs. Additional circumstances favoring the superstorm were (i) the exact impact of the spheromak on the Earth's magnetosphere and (ii) the almost exact southward orientation of the magnetic field, corresponding to the original orientation in its probable source region near the solar disk center.

Authors: V. V. Grechnev, A. M. Uralov, I. M. Chertok, A. V. Belov, B. P. Filippov, V. A. Slemzin, B. V. Jackson
Projects: ACE,Neutron Monitors,Other

Publication Status: Solar Phys., accepted
Last Modified: 2014-09-03 13:11
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A Challenging Solar Eruptive Event of 18 November 2003 and the Causes of the 20 November Geomagnetic Superstorm. III. Catastrophe of the Eruptive Filament in a Magnetic Null Point and Formation of an Opposite-Handedness CME  

Victor Grechnev   Submitted: 2014-04-14 23:33

Our analysis in Papers I and II (Grechnev et al., 2014, Solar Phys. 289, 289 and 1279) of the 18 November 2003 solar event responsible for the 20 November geomagnetic superstorm has revealed a complex chain of eruptions. In particular, the eruptive filament encountered a topological discontinuity located near the solar disk center at a height of about 100 Mm, bifurcated, and transformed into a large cloud, which did not leave the Sun. Concurrently, an additional CME presumably erupted close to the bifurcation region. The conjectures about the responsibility of this compact CME for the superstorm and its disconnection from the Sun are confirmed in Paper IV (Grechnev et al., Solar Phys., submitted), which concludes about its probable spheromak-like structure. The present paper confirms the presence of a magnetic null point near the bifurcation region and addresses the origin of the magnetic helicity of the interplanetary magnetic clouds and their connection to the Sun. We find that the orientation of a magnetic dipole constituted by dimmed regions with the opposite magnetic polarities away from the parent active region corresponded to the direction of the axial field in the magnetic cloud, while the pre-eruptive filament mismatched it. To combine all of the listed findings, we come to an intrinsically three-dimensional scheme, in which a spheromak-like eruption originates via the interaction of the initially unconnected magnetic fluxes of the eruptive filament and pre-existing ones in the corona. Through a chain of magnetic reconnections their positive mutual helicity was transformed into the self-helicity of the spheromak-like magnetic cloud.

Authors: Uralov, A.M., Grechnev, V.V., Rudenko, G.V., Myshyakov, I.I., Chertok, I.M., Filippov, B.P., Slemzin, V.A.
Projects: CORONAS-F,GOES X-rays ,Other,SoHO-EIT,SoHO-MDI,SoHO-LASCO,TRACE

Publication Status: Solar Phys., accepted
Last Modified: 2014-04-16 13:15
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A Challenging Solar Eruptive Event of 18 November 2003 and the Causes of the 20 November Geomagnetic Superstorm. II. CMEs, Shock Waves, and Drifting Radio Bursts  

Victor Grechnev   Submitted: 2013-08-15 00:32

We continue our study (Grechnev et al. (2013), doi:10.1007/s11207-013-0316-6; Paper I) on the 18 November 2003 geoffective event. To understand possible impact on geospace of coronal transients observed on that day, we investigated their properties from solar near-surface manifestations in extreme ultraviolet, LASCO white-light images, and dynamic radio spectra. We reconcile near-surface activity with the expansion of coronal mass ejections (CMEs) and determine their orientation relative to the earthward direction. The kinematic measurements, dynamic radio spectra, and microwave and X-ray light curves all contribute to the overall picture of the complex event and confirm an additional eruption at 08:07-08:20 UT close to the solar disk center presumed in Paper I. Unusual characteristics of the ejection appear to match those expected for a source of the 20 November superstorm but make its detection in LASCO images hopeless. On the other hand, none of the CMEs observed by LASCO seem to be a promising candidate for a source of the superstorm being able to produce, at most, a glancing blow on the Earth's magnetosphere. Our analysis confirms free propagation of shock waves revealed in the event and reconciles their kinematics with ''EUV waves'' and dynamic radio spectra up to decameters.

Authors: V.V. Grechnev, A.M. Uralov, I.M. Chertok, V.A. Slemzin, B.P. Filippov, Ya.I. Egorov, V.G. Fainshtein, A.N. Afanasyev, N.P. Prestage, M. Temmer
Projects: CORONAS-F,GOES X-rays ,Other,RHESSI,SoHO-EIT,SoHO-LASCO,SXI

Publication Status: Solar Phys., accepted
Last Modified: 2013-08-15 07:53
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An Updated View of Solar Eruptive Flares and Development of Shocks and CMEs: History of the 2006 December 13 GLE-Productive Extreme Event  

Victor Grechnev   Submitted: 2013-08-13 21:20

An extreme 2006 December 13 event marked the onset of the Hinode era being the last major flare in the solar cycle 23 observed with NoRH and NoRP. The event produced a fast CME, strong shock, and big particle event responsible for GLE70. We endeavor to clarify relations between eruptions, shock wave, and the flare, and to shed light on a debate over the origin of energetic protons. One concept relates it with flare processes. Another one associates acceleration of ions with a bow shock driven by a CME at (2-4)R_sun. The latter scenario is favored by a delayed particle release time after the flare. However, our previous studies have established that a shock wave is typically excited by an impulsively erupting magnetic rope (future CME core) during the flare rise, while the outer CME surface evolves from an arcade whose expansion is driven from inside. Observations of the 2006 December 13 event reveal two shocks following each other, whose excitation scenario contradicts the delayed CME-driven bow-shock hypothesis. Actually, the shocks developed much earlier, and could accelerate protons still before the flare peak. Then, the two shocks merged into a single stronger one and only decelerated and dampened long afterwards.

Authors: V. Grechnev, V. Kiselev, A. Uralov, N. Meshalkina, A. Kochanov
Projects: GOES X-rays ,Hinode/SOT,Hinode/XRT,Nobeyama Radioheliograph,RHESSI,SoHO-EIT,SoHO-MDI,SoHO-LASCO,SXI

Publication Status: Accepted for publication in PASJ
Last Modified: 2013-08-14 08:28
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Microwave Negative Bursts as Indications of Reconnection between Eruptive Filaments and Large-Scale Coronal Magnetic Environment  

Victor Grechnev   Submitted: 2013-08-13 01:37

Low-temperature plasma ejected in solar eruptions can screen active regions as well as quiet solar areas. Absorption phenomena can be observed in microwaves as 'negative bursts' and in different spectral domains. We analyze two very different recent events with such phenomena and present an updated systematic view of solar events associated with negative bursts. Related filament eruptions can be normal, without essential changes of shape and magnetic configuration, and 'anomalous'. The latter are characterized by disintegration of an eruptive filament and dispersal of its remnants as a cloud over a large part of solar disk. Such phenomena can be observed as giant depressions in the He II 304 Å line. One of possible scenarios for an anomalous eruption is proposed in terms of reconnection of filament's internal magnetic fields with external large-scale coronal surrounding.

Authors: V. Grechnev, I. Kuzmenko, A. Uralov, I. Chertok, A. Kochanov
Projects: Nobeyama Radioheliograph,Other,SDO-AIA,SoHO-EIT,SoHO-LASCO,STEREO

Publication Status: PASJ, accepted
Last Modified: 2013-08-13 11:02
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Relations between strong high-frequency microwave bursts and proton events  

Victor Grechnev   Submitted: 2013-08-13 01:23

Proceeding from close association between solar eruptions, flares, shock waves, and CMEs, we analyze relations between bursts at 35 GHz recorded with the Nobeyama Radio Polarimeters during 1990-2012, on the one hand, and solar energetic particle (SEP) events, on the other hand. Most west to moderately east solar events with strong bursts at 35 GHz produced near-Earth proton enhancements of J(E > 100 MeV) > 1 pfu. The strongest and hardest those caused ground level enhancements. There is a general, although scattered, correspondence between proton enhancements and peak fluxes at 35 GHz, especially pronounced if the 35 GHz flux exceeds 104 sfu and the microwave peak frequency is high. These properties indicate emission from numerous high-energy electrons in very strong magnetic fields suggesting a high rate of energy release in the flare-CME formation process. Flaring above the sunspot umbra appears to be typical of such events. Irrespective of the origin of SEPs, these circumstances demonstrate significant diagnostic potential of high-frequency microwave bursts and sunspot-associated flares for space weather forecasting. Strong prolonged bursts at 35 GHz promptly alert to hazardous SEP events with hard spectra. A few exceptional events with moderate bursts at 35 GHz and strong proton fluxes look challenging and should be investigated.

Authors: V. Grechnev, N. Meshalkina, I. Chertok, V. Kiselev
Projects: GOES Particles,GOES X-rays ,Hinode/SOT,Neutron Monitors,Nobeyama Radioheliograph,Owens Valley Solar Array,SDO-AIA,SoHO-MDI,TRACE,Yohkoh-HXT

Publication Status: PASJ, accepted
Last Modified: 2013-08-13 11:02
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A Challenging Solar Eruptive Event of 18 November 2003 and the Causes of the 20 November Geomagnetic Superstorm. I. Unusual History of an Eruptive Filament  

Victor Grechnev   Submitted: 2013-05-02 08:34

This is the first of four companion papers, which analyze a complex eruptive event of 18 November 2003 in AR 10501 and the causes of the largest Solar Cycle 23 geomagnetic storm on 20 November 2003. Analysis of a complete data set, not considered before, reveals a chain of eruptions to which hard X-ray and microwave bursts responded. A filament in AR 10501 was not a passive part of a larger flux rope, as usually considered. The filament erupted and gave origin to a CME. The chain of events was as follows: i) an eruption at 07:29 accompanied by a not reported M1.2 class flare associated with the onset of a first southeastern CME1, which is not responsible for the superstorm; ii) a confined eruption at 07:41 (M3.2 flare) that destabilized the filament; iii) the filament acceleration (07:56); iv) the bifurcation of the eruptive filament that transformed into a large cloud; v) an M3.9 flare in AR 10501 associated to this transformation. The transformation of the filament could be due to its interaction with the magnetic field in the neighborhood of a null point, located at a height of about 100 Mm above the complex formed by ARs 10501, 10503, and their environment. The CORONAS-F/SPIRIT telescope observed the cloud in 304 Å as a large Y-shaped darkening, which moved from the bifurcation region to the limb. The masses and kinematics of the cloud and the filament were similar. Remnants of the filament were not observed in the second southwestern CME2, previously regarded as a source of the 20 November superstorm. These facts do not support a simple scenario, in which the interplanetary magnetic cloud is considered as a flux rope formed from a structure initially associated with the pre-eruption filament in AR 10501. Observations suggest a possible additional eruption above the bifurcation region close to solar disk center between 08:07 and 08:17 that could be the source of the superstorm.

Authors: V. V. Grechnev, A. M. Uralov, V. A. Slemzin, I. M. Chertok, B. P. Filippov, G. V. Rudenko, M. Temmer
Projects: SoHO-EIT

Publication Status: Solar Physics, accepted
Last Modified: 2013-05-03 13:16
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Coronal Shock Waves, EUV waves, and Their Relation to CMEs. I. Reconciliation of ''EIT waves'', Type II Radio Bursts, and Leading Edges of CMEs  

Victor Grechnev   Submitted: 2011-04-18 19:49

We show examples of excitation of coronal waves by flare-related abrupt eruptions of magnetic rope structures. The waves presumably rapidly steepened into shocks and freely propagated afterwards like decelerating blast waves that showed up as Moreton waves and EUV waves. We propose a simple quantitative description for such shock waves to reconcile their observed propagation with drift rates of metric type II bursts and kinematics of leading edges of coronal mass ejections (CMEs). Taking account of different plasma density falloffs for propagation of a wave up and along the solar surface, we demonstrate a close correspondence between drift rates of type II bursts and speeds of EUV waves, Moreton waves, and CMEs observed in a few known events.

Authors: V. V. Grechnev, A. M. Uralov, I. M. Chertok, I. V. Kuzmenko, A. N. Afanasyev, N. S. Meshalkina, S. S. Kalashnikov, Y. Kubo
Projects: TRACE

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2011-04-19 06:30
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Coronal Shock Waves, EUV Waves, and Their Relation to CMEs. III. Shock-Associated CME/EUV Wave in an Event with a Two-Component EUV Transient  

Victor Grechnev   Submitted: 2011-04-18 19:45

On 17 January 2010, STEREO-B observed in extreme ultraviolet (EUV) and white light a large-scale dome-shaped expanding coronal transient with perfectly connected off-limb and on-disk signatures. Veronig et al. (2010, ApJL 716, 57) concluded that the dome was formed by a weak shock wave. We have revealed two EUV components, one of which corresponded to this transient. All of its properties found from EUV, white light, and a metric type II burst match expectations for a freely expanding coronal shock wave including correspondence to the fast-mode speed distribution, while the transient sweeping over the solar surface had a speed typical of EUV waves. The shock wave was presumably excited by an abrupt filament eruption. Both a weak shock approximation and a power-law fit match kinematics of the transient near the Sun. Moreover, the power-law fit matches expansion of the CME leading edge up to 24 solar radii. The second, quasi-stationary EUV component near the dimming was presumably associated with a stretched CME structure; no indications of opening magnetic fields have been detected far from the eruption region.

Authors: V. V. Grechnev, A. N. Afanasyev, A. M. Uralov, I. M. Chertok, M. V. Eselevich, V. G. Eselevich, G. V. Rudenko, Y. Kubo
Projects: STEREO

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2011-04-19 06:30
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Solar flare-related eruptions followed by long-lasting occultation of the emission in the He II 304 Å line and in microwaves  

Victor Grechnev   Submitted: 2011-03-24 17:23

Plasma with a temperature close to the chromospheric one is ejected in solareruptions. Such plasma can occult some part of emission of compact sources inactive regions as well as quiet solar areas. Absorption phenomena can beobserved in the microwave range as the so-called 'negative bursts' and also inthe He II 304 Å line. The paper considers three eruptive events associated withrather powerful flares. Parameters of absorbing material of an eruption areestimated from multi-frequency records of a 'negative burst' in one event.'Destruction' of an eruptive filament and its dispersion like a cloud over ahuge area observed as a giant depression of the 304 Å line emission has beenrevealed in a few events. One such event out of three ones known to us isconsidered in this paper. Another event is a possibility.

Authors: V. V. Grechnev, I. V. Kuzmenko, I. M. Chertok, A. M. Uralov
Projects:

Publication Status: 2011 Accepted by Astronomy Reports
Last Modified: 2011-04-10 22:26
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An Extreme Solar Event of 20 January 2005: Properties of the Flare and the Origin of Energetic Particles  

Victor Grechnev   Submitted: 2008-06-30 03:14

The famous extreme solar and particle event of 20 January 2005 is analyzed from two perspectives. Firstly, using multi-spectral data, we study temporal, spectral, and spatial features of the main phase of the flare, when the strongest emissions from microwaves up to 200 MeV gamma-rays were observed. Secondly, we relate our results to a long-standing controversy on the origin of solar energetic particles (SEP) arriving at Earth, i.e., acceleration in flares, or shocks ahead of coronal mass ejections (CMEs). Our analysis shows that all electromagnetic emissions from microwaves up to 2.22 MeV line gamma-rays during the main flare phase originated within a compact structure located just above sunspot umbrae. In particular, a huge (~105 sfu) radio burst with a high frequency maximum at 30 GHz was observed, indicating the presence of a large number of energetic electrons in very strong magnetic fields. Thus, protons and electrons responsible for various flare emissions during its main phase were accelerated within the magnetic field of the active region. The leading, impulsive parts of the ground-level enhancement (GLE), and highest-energy gamma-rays identified with pi^0-decay emission, are similar and closely correspond in time. The origin of the pi^0-decay gamma-rays is argued to be the same as that of lower-energy emissions, although this is not proven. On the other hand, we estimate the sky-plane speed of the CME to be 2000-2600 km s-1, i.e., high, but of the same order as preceding non-GLE-related CMEs from the same active region. Hence, the flare itself rather than the CME appears to determine the extreme nature of this event. We therefore conclude that the acceleration, at least, to sub-relativistic energies, of electrons and protons, responsible for both the major flare emissions and the leading spike of SEP/GLE by 07 UT, are likely to have occurred nearly simultaneously within the flare region. However, our analysis does not rule out a probable contribution from particles accelerated in the CME-driven shock for the leading GLE spike, which seemed to dominate at later stages of the SEP event.

Authors: Grechnev, V. V., Kurt, V. G., Chertok, I. M., Uralov A. M. , Nakajima, H., Altyntsev A. T., Belov, A. V., Yushkov, B. Yu., Kuznetsov, S. N., Kashapova, L. K., Meshalkina, N. S., Prestage, N. P.
Projects: RHESSI,SoHO-EIT,SoHO-MDI,SoHO-LASCO,TRACE

Publication Status: Solar Physics, v. 252(1), pp. 149-177, 2008, DOI: 10.1007/s11207-008-9245-1. The original publication is available at www.springerlink.com
Last Modified: 2009-09-02 00:05
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Subject will be restored when possible  

Victor Grechnev   Submitted: 2008-03-27 19:57

Neutral Line associated Sources (NLS) are quasi-stationary microwave sources projected onto vicinities of the neutral line of the photospheric magnetic field. NLS are often precursors of powerful flares, but their nature is unclear. We endeavor to reveal the structure of an NLS and to analyze a physical connection between such a source with a site of energy release in the corona above NOAA 10488 (October/November 2003). Evolution of this AR includes emergence and collision of two bipolar magnetic structures, rise of the main magnetic separator, and the appearance of an NLS underneath. The NLS appears at a contact site of colliding sunspots, whose relative motion goes on, resulting in large shear along a tangent. Then the nascent NLS becomes the main source of microwave fluctuations in the AR. The NLS emission at 17 GHz is dominated by either footpoints, or the top of a loop-like structure, an NLS loop, which connects two colliding sunspots. During a considerable amount of time, the emission dominates over that footpoint of the NLS loop, where the magnetic field is stronger. At that time, the NLS resembles a usual sunspot-associated radio source, whose brightness center is displaced towards the periphery of a sunspot. Microwave emission of an X2.7 flare is mainly concentrated in an ascending flare loop, initially coinciding with the NLS loop. The top of this loop is located at the base of a non-uniform bar-like structure visible in soft X-rays and at 34 GHz at the flare onset. We reveal (i) upward lengthening of this bar before the flare onset, (ii) the motion of the top of an apparently ascending flare loop along the axis of this bar, and (iii) a non-thermal microwave source, whose descent along the bar was associated with the launching of a coronal ejection. We connect the bar with a probable position of a nearly vertical diffusion region, a site of maximal energy release inside an extended pre-flare current sheet. The top of the NLS loop is located at the bottom of this region. A combination of the NLS loop and diffusion region constitutes the skeleton of a quasi-stationary microwave NLS.

Authors: A.M.Uralov, V.V.Grechnev, G.V.Rudenko, I.G.Rudenko, H.Nakajima
Projects: SoHO-MDI,SoHO-LASCO

Publication Status: Solar Physics, accepted
Last Modified: 2008-03-28 12:29
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Subject will be restored when possible  

Victor Grechnev   Submitted: 2008-03-27 19:57

Neutral Line associated Sources (NLS) are quasi-stationary microwave sources projected onto vicinities of the neutral line of the photospheric magnetic field. NLS are often precursors of powerful flares, but their nature is unclear. We endeavor to reveal the structure of an NLS and to analyze a physical connection between such a source with a site of energy release in the corona above NOAA 10488 (October/November 2003). Evolution of this AR includes emergence and collision of two bipolar magnetic structures, rise of the main magnetic separator, and the appearance of an NLS underneath. The NLS appears at a contact site of colliding sunspots, whose relative motion goes on, resulting in large shear along a tangent. Then the nascent NLS becomes the main source of microwave fluctuations in the AR. The NLS emission at 17 GHz is dominated by either footpoints, or the top of a loop-like structure, an NLS loop, which connects two colliding sunspots. During a considerable amount of time, the emission dominates over that footpoint of the NLS loop, where the magnetic field is stronger. At that time, the NLS resembles a usual sunspot-associated radio source, whose brightness center is displaced towards the periphery of a sunspot. Microwave emission of an X2.7 flare is mainly concentrated in an ascending flare loop, initially coinciding with the NLS loop. The top of this loop is located at the base of a non-uniform bar-like structure visible in soft X-rays and at 34 GHz at the flare onset. We reveal (i) upward lengthening of this bar before the flare onset, (ii) the motion of the top of an apparently ascending flare loop along the axis of this bar, and (iii) a non-thermal microwave source, whose descent along the bar was associated with the launching of a coronal ejection. We connect the bar with a probable position of a nearly vertical diffusion region, a site of maximal energy release inside an extended pre-flare current sheet. The top of the NLS loop is located at the bottom of this region. A combination of the NLS loop and diffusion region constitutes the skeleton of a quasi-stationary microwave NLS.

Authors: A.M.Uralov, V.V.Grechnev, G.V.Rudenko, I.G.Rudenko, H.Nakajima
Projects: SoHO-MDI,SoHO-LASCO

Publication Status: Solar Physics, accepted, DOI: 10.1007/s11207-008-9183-y. The original publication is available at www.springerlink.com
Last Modified: 2008-09-23 21:12
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Victor Grechnev   Submitted: 2008-03-26 22:05

We present a case study of the 13 July 2004 solar event, in which disturbances caused by eruption of a filament from an active region embraced a quarter of the visible solar surface. Remarkable are absorption phenomena observed in the SOHO/EIT 304 Å channel; they were also visible in the EIT 195 A channel, in the Hα line, and even in total radio flux records. Coronal and Moreton waves were also observed. Multi-spectral data allowed reconstructing an overall picture of the event. An explosive filament eruption and related impulsive flare produced a CME and blast shock, both of which decelerated and propagated independently. Coronal and Moreton waves were kinematically close and both decelerated in accordance with an expected motion of the coronal blast shock. The CME did not resemble a classical three-component structure, probably, because some part of the ejected mass fell back onto the Sun. Quantitative evaluations from different observations provide close estimates of the falling mass, ~3*1015 g, which is close to the estimated mass of the CME. The falling material was responsible for the observed large-scale absorption phenomena, in particular, shallow widespread moving dimmings observed at 195 A. By contrast, deep quasi-stationary dimmings observed in this band near the eruption center were due to plasma density decrease in coronal structures.

Authors: V.V.Grechnev, A.M.Uralov, V.A.Slemzin, I.M.Chertok, I.V.Kuzmenko, K.Shibasaki
Projects: SoHO-EIT,SoHO-LASCO,TRACE

Publication Status: Solar Physics, accepted, DOI: 10.1007/s11207-008-9178-8. The original publication is available at www.springerlink.com
Last Modified: 2008-09-23 21:12
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