fl237.farnik03 Posted: 07-Jul-96 Updated: Events specified: N/A
F. Farnik and S. Savy
Motivation:
The role of the preflare processes in relation to the driving
flare mechanism is still poorly understood. Not many studies
of the topic have been undertaken so far. It was shown recently
(Farnik et al. Sol. Phys. 165:169-179 1996) that SXT observations
place the preflare emission source roughly at the same altitude
level where the main flare later appears, close to the main source
but not necessarily at the same position. Even when the pre-flaring
activity (emission) is mostly very weak (only appr. 25% of flares
have pronounced x-ray and radio preflares) and in most cases it can
be below the instrument sensitivity limit, it may play an important
role in the flare energy release process.
Required observations: BCS, SXT, HXT
Analysis technigues:
Using BCS, SXT and HXT data we propose to study the activity of coronal
loop structures prior to the occurrance of flares in those regions. SXT
images will enable us to study the spatial relationship between preflare
activity in the same active region and subsequent flare sources as well
as to sort over four years of Yohkoh data by rejecting those events in
which the two sources are in different active regions and have no obvious
physical relation. The techinique of constructing SXT difference images
will be used to study the timing of spatially distinct brightenings and
changes in active region structure and dynamics.
In some events the preflare source intensity may be expected to be high
enough to enable hard X-ray image reconstruction and BCS spectral analysis.
We also hope important knowledge will be derived from high-resolution
magnetograms (Kitt Peak) and their co-alignment with X-ray images. Among
other things, we will be investigating:
(i) The degree to which flare loop structures are active prior to the
occurrance of a flare, and the nature of this activity.
(ii) Evidence for dynamical evolution and activation of higher altitude
or larger coronal structures prior to and at the onset of flares.
(iii) Evidence for chromospheric evaporation prior to the main (hard) phase of solar flares, and the spectral characteristics of hard X-ray emission before the main phase.