Critical issues for understanding particle acceleration in impulsive solar flares

Abstract

Abstract. This paper, a review of the present status of existing models for particle acceleration during impulsive solar flares, was inspired by a week-long workshop held in the Fall of 1993 at NASA Goddard Space Flight Center. Recent observations from Yohkoh and the Compton Gamma Ray Observatory, and a reanalysis of older observations from the Solar Maximum Mission, have led to important new results concerning the location, timing, and eificiency of particle acceleration in flares. These are summarized in the first part of the review. Particle acceleration processes are then discussed, with particular emphasis on new developments in stochastic acceleration by magnetohydrodynamic waves and direct electric field acceleration by both sub-and super-Dreicer electric fields. Finally, issues that arise when these mechanisms are incorporated into the large-scale flare structure are considered. Stochastic and super-Dreicer acceleration may occur either in a single large coronal reconnection site or at multiple "fragmented" energy release sites. Sub-Dreicer acceleration requires a highly filamented coronal current pattern. A particular issue that needs to be confronted by all theories is the apparent need for large magnetic field strengths in the flare energy release region.

Probability of Solar Flares Turn out to Form a Coronal Mass Ejections Events due to the Characterization of Solar Radio Burst Type II and III

“…The motion of the shock through the radial plasma International Letters of Chemistry, Physics and Astronomy Vol. 35 21 density profile can be observed based on the decreasing of the signal in frequency. One can deduce the propagation speed of the driving shock wave from eruption region.…”

“…A new experiment approach by e-CALLISTO with 24 hours International Letters of Chemistry, Physics and Astronomy Vol. 35monitoring and further development of a model of the theory are hoping to meet the current knowledge about the Sun behaviour.…”

“…In the solar corona, there are many particle acceleration phenomena that are caused by the interaction between coronal International Letters of Chemistry, Physics and Astronomy Vol. 35magnetic field and plasma. The non-thermal electrons accelerated in the solar corona emit radio waves in the metric range resulting in many types of observed solar radio burst [106].…”

“…However, the most popular classes of mechanisms for electrons are accelerated by an electric field parallel to the magnetic field by shocks and stochastic acceleration by waves [35]. There is also a complete scenario that can explain flare electron acceleration by a self-consistent chain of sub-processes.…”

“…It should be noted that observations show that Langmuir waves associated with solar type III radio bursts International Letters of Chemistry, Physics and Astronomy Vol. 35are highly localized [202,203]. One fundamental theory, it is believed is that Landau resonance with the unstable electron beam is responsible generates Langmuir waves, which are thought to undergo nonlinear wave-wave interactions that produce electromagnetic emissions at the local electron plasma frequency (f pe ) and its second harmonic (2f pe ) [190,194,[204][205][206][207].…”