Thermal trigger for solar flares and coronal loops formation

Solar Physics ◽  
1982 ◽  
Vol 75 (1-2) ◽  
pp. 237-244 ◽  
Author(s):  
B. V. Somov ◽  
S. I. Syrovatskii
Keyword(s):  
Solar Flares ◽  
Coronal Loops

scholarly journals HXR photospheric footprints

2007 ◽  
Vol 3 (S247) ◽  
pp. 110-113
Author(s):  
J. C. Martínez-Oliveros ◽  
A.-C. Donea ◽  
P. S. Cally
Keyword(s):  
Solar Flares ◽  
Acoustic Waves ◽  
Neutral Line ◽  
Impulsive Phase ◽  
Coronal Loops ◽  
Direct Link ◽  
Constructive Interference ◽  
X Ray ◽  
Hydrodynamic Response ◽  
Relativistic Particles

AbstractWe have analysed the 6 mHz egression power signatures of some accoustically active X-class solar flares. During the impulsive phase these flares produced conspicuous seismic signatures which have kernel-like structures, mostly aligned with the neutral line of the host active region. The kernel-like structures show the effect of constructive interference of the acoustic waves emanating from the complex sources, suggesting motion of the acoustic sources. The co-aligment between the seismic signatures and the hard X-ray emission observed by RHESSI from the footpoints of the coronal loops suggests a direct link between relativistic particles accelerated during the flare and the hydrodynamic response of the photosphere during flares.

scholarly journals Post-flare Coronal Activity on AU Mic Detected by EUVE

1995 ◽  
Vol 151 ◽  
pp. 146-147
Author(s):  
Maria Katsova ◽  
Jeremy Drake ◽  
Moissei Livshits
Keyword(s):  
Solar Flares ◽  
Extreme Ultraviolet ◽  
Emission Measure ◽  
Coronal Loops ◽  
Stellar Radius ◽  
Euv Emission ◽  
Long Duration ◽  
Red Dwarfs ◽  
Coronal Activity ◽  
Region Scale

Data of long-duration emission arising after the impulsive rise and decay in a flaring event on the red dwarf star AU Mic are discussed. Intensive EUV emission in the band 65-190 Å was registered by the Extreme Ultraviolet Explorer (EUVE) after both impulses during half a day. A similar behavior of the flux in the Fe XVIII 93.9 Å line is detected after the first powerful impulse. The decay of the intensity in the 65-190 Å band and in the Fe XVIII line during this prolonged event is 10 times slower than the time of radiative cooling of coronal loops with a typical flare plasma density. Some difficulties with two explanations of this event proposed earlier are discussed. Explanation (i) - the radiation of dense loops at main phase of the flare, and (ii) - the emission of the low-dense plasma of coronal transients (CME). The temporal behavior of the emission measure is determined for both the 65-190 Å band and the Fe XVIII line fluxes. The total energy emitted in the 1-2000 Å region for the long-duration event lasting almost 12 hours is 3 · 1035 ergs. The following physical model is proposed to explain the prolonged event (Fig. 1): the source of emission is the system of high coronal loops, the size of which is more than the active region scale, but is less than the stellar radius. The temperature of the plasma in the loops decreases from 107 K slowly, during a few hours. The densities in these loops are in the range 1013 cm−3 to 5 · 109 cm−3. Such systems, when the plasma therein becomes cool, are observed in the Hα line during large solar flares (for instance, June 15, 1991) after CME. Some additional post-flare energy input into this high coronal loop systems can be caused by the reconnection in vertical current sheet, and this post-eruptive energy release provides prolonged and intensive EUV emission.Apparently, we are faced here with a new kind of surface activity on late-type stars which is intermediate between impulsive flares on red dwarfs and long-duration, powerful events on subgiants, which are components of RS CVn binaries.The full version of this contribution will be published in Astronomicheskij Zhurnal (Astronomy Reports), 1995, Vol. 72.

scholarly journals Flare particle acceleration in the interaction of twisted coronal flux ropes

2018 ◽  
Vol 611 ◽  
pp. A40 ◽  
Author(s):  
J. Threlfall ◽  
A. W. Hood ◽  
P. K. Browning
Keyword(s):  
Particle Acceleration ◽  
Solar Flares ◽  
Three Dimensional ◽  
Coronal Loops ◽  
Mhd Simulation ◽  
Mhd Simulations ◽  
Uniform Background ◽  
Energy Gains ◽  
Particle Behaviour

Aim. The aim of this work is to investigate and characterise non-thermal particle behaviour in a three-dimensional (3D) magnetohydrodynamical (MHD) model of unstable multi-threaded flaring coronal loops.Methods. We have used a numerical scheme which solves the relativistic guiding centre approximation to study the motion of electrons and protons. The scheme uses snapshots from high resolution numerical MHD simulations of coronal loops containing two threads, where a single thread becomes unstable and (in one case) destabilises and merges with an additional thread.Results. The particle responses to the reconnection and fragmentation in MHD simulations of two loop threads are examined in detail. We illustrate the role played by uniform background resistivity and distinguish this from the role of anomalous resistivity using orbits in an MHD simulation where only one thread becomes unstable without destabilising further loop threads. We examine the (scalable) orbit energy gains and final positions recovered at different stages of a second MHD simulation wherein a secondary loop thread is destabilised by (and merges with) the first thread. We compare these results with other theoretical particle acceleration models in the context of observed energetic particle populations during solar flares.

scholarly journals Commission 10: Solar Activity

2005 ◽  
Vol 1 (T26A) ◽  
pp. 75-88
Author(s):  
Donald B. Melrose ◽  
James A. Klimchuk ◽  
A.O. Benz ◽  
I.J.D. Craig ◽  
N. Gopalswamy ◽  
...  
Keyword(s):  
Solar Activity ◽  
Space Weather ◽  
Coronal Mass Ejections ◽  
Solar Flares ◽  
Interplanetary Space ◽  
Coronal Loops ◽  
Theoretical Concepts ◽  
Near Earth Space ◽  
Solar Observations ◽  
Extensive List

AbstractCommission 10 aims at the study of various forms of solar activity, including networks, plages, pores, spots, fibrils, surges, jets, filaments/prominences, coronal loops, flares, coronal mass ejections (CMEs), solar cycle, microflares, nanoflares, coronal heating etc., which are all manifestation of the interplay of magnetic fields and solar plasma. Increasingly important is the study of solar activities as sources of various disturbances in the interplanetary space and near-Earth “space weather”.Over the past three years a major component of research on the active Sun has involved data from the RHESSI spacecraft. This review starts with an update on current and planned solar observations from spacecraft. The discussion of solar flares gives emphasis to new results from RHESSI, along with updates on other aspects of flares. Recent progress on two theoretical concepts, magnetic reconnection and magnetic helicity is then summarized, followed by discussions of coronal loops and heating, the magnetic carpet and filaments. The final topic discussed is coronal mass ejections and space weather.The discussions on each topic is relatively brief, and intended as an outline to put the extensive list of references in context.The review was prepared jointly by the members of the Organizing Committee, and the names of the primary contributors to the various sections are indicated in parentheses.

Kink instability of solar coronal loops as the cause of solar flares

Solar Physics ◽  
1979 ◽  
Vol 64 (2) ◽  
pp. 303-321 ◽  
Author(s):  
A. W. Hood ◽  
E. R. Priest
Keyword(s):  
Solar Flares ◽  
Coronal Loops ◽  
Kink Instability ◽  
Solar Coronal

scholarly journals VLA Observations of the Coronal Plasma

1990 ◽  
Vol 142 ◽  
pp. 501-507
Author(s):  
Kenneth R. Lang
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Solar Flares ◽  
Thermal Emission ◽  
Active Regions ◽  
The Other ◽  
Physical Parameters ◽  
Coronal Loops ◽  
Radiation Mechanisms ◽  
X Ray

VLA observations at 20-cm wavelength specify the brightness temperature and magnetic structure of plasma constrained within coronal loops in solar active regions. Comparisons with simultaneous SMM observations at soft X-ray wavelengths lead to measurements of physical parameters like electron density, electron temperature and magnetic field strength. Such comparisons also indicate coronal loops can be detected at either radio or X-ray wavelengths while remaining invisible in the other spectral domain, and that the dominant radiation mechanisms can be thermal bremsstrahlung or thermal gyroresonance radiation. VLA observations at the longer 90-cm wavelength reveal the thermal emission of a hot transition sheath enveloping a cooler, underlying Hα filament seen in absorption. The 20-cm VLA observations indicate that the precursor, impulsive and post-flare components of solar flares originate in spatially separated and resolved sources.

scholarly journals Magnetohydrodynamic waves and coronal seismology: an overview of recent results

2012 ◽  
Vol 370 (1970) ◽  
pp. 3193-3216 ◽  
Author(s):  
Ineke De Moortel ◽  
Valery M. Nakariakov
Keyword(s):  
Solar Atmosphere ◽  
Solar Flares ◽  
Mhd Waves ◽  
Alfvén Waves ◽  
Coronal Loops ◽  
Magnetohydrodynamic Waves ◽  
Coronal Seismology ◽  
Wide Range ◽  
Current Controversy ◽  
Intense Debate

Recent observations have revealed that magnetohydrodynamic (MHD) waves and oscillations are ubiquitous in the solar atmosphere, with a wide range of periods. We give a brief review of some aspects of MHD waves and coronal seismology that have recently been the focus of intense debate or are newly emerging. In particular, we focus on four topics: (i) the current controversy surrounding propagating intensity perturbations along coronal loops, (ii) the interpretation of propagating transverse loop oscillations, (iii) the ongoing search for coronal (torsional) Alfvén waves, and (iv) the rapidly developing topic of quasi-periodic pulsations in solar flares.

Radial oscillations of coronal loops and microwave radiation from solar flares

2002 ◽  
Vol 28 (11) ◽  
pp. 783-791 ◽  
Author(s):  
Yu. G. Kopylova ◽  
A. V. Stepanov ◽  
Yu. T. Tsap
Keyword(s):  
Microwave Radiation ◽  
Solar Flares ◽  
Coronal Loops

Siphon Flows in Stratified Coronal Loops

1994 ◽  
Vol 144 ◽  
pp. 185-187
Author(s):  
S. Orlando ◽  
G. Peres ◽  
S. Serio
Keyword(s):  
Heat Flux ◽  
Scaling Laws ◽  
Flow Model ◽  
Supersonic Flows ◽  
Coronal Loops ◽  
Characteristic Parameters

AbstractWe have developed a detailed siphon flow model for coronal loops. We find scaling laws relating the characteristic parameters of the loop, explore systematically the space of solutions and show that supersonic flows are impossible for realistic values of heat flux at the base of the upflowing leg.

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