RHESSI/SOHO/TRACE Workshop

WG1: Pre-Event Physics

This group will focus on pre-event physics, and aims to reveal the causal relationship between  photospheric (and sub-photospheric) processes and  subsequent flare and CME energy release.   The two basic questions that define the scope of this working group are:
The group activity will include discussions of observations, techniques, theory and numerical simulations.  We will discuss both recent results and new methodologies including, for instance, local helioseismology and the measurement of velocities and magnetic fields associated with magnetic helicity emergence. 

Questions

1. How is  free magnetic energy built up in the solar corona? 

2. What type of photospheric activities trigger solar flares and CMEs? 

3. What can we learn about the pre-event physics from local correlation tracking,  vector magnetogram  and the local helioseismology techniques?

4. How do precursor phenomena and pre-flare heating, e.g. observed by TRACE 1600A, related to the subsequent flare events?

Observations

Although there are many observations of pre-event processes, the physical relationship between these processes and the subsequent flare and CME events is not yet well understood. The main reason for that is attributed to the fact that the important physical process in the pre-event phase may be invisible. Several new methodologies, which detect photospheric and subphotospheric flows, have recently been developed. One is the direct measurement of energy and helicity fluxes through the photospheric surface based on the vector magnetograms, and another is the local helioseismology technique. We will discuss what we have learned from such measurements recently, and what we can learn from them in the near future.  We will also discuss the physical relationship between quantitative measurements of magnetic energy and helicity and the morphological observation by X-ray, UV, and Halpha in pre-event phase.

Theory and modeling

Theoretically, eruptive flare events might be understood as a consequence of a loss-of-stability process or a loss-of-equilibrium process. Although many such theoretical models have been proposed, it is still arguable which process is most important for triggering flares.  3D modeling is very useful to study this problem. Actually, several 3D MHD simulations including practical photospheric and sub-photospheric activities have been developed recently. The mutual communication between model-based studies and the results of data analyses is crucial to understand the underlying physics.

Events and active regions for study