Characteristics of Solar Flare Hard X-ray Emissions: Observations and Models
Wei Liu Submitted: 2006-12-21 01:12
The main theme of this thesis is the investigation of the physics of
acceleration and transport of particles in solar flares, and
their thermal and nonthermal radiative signatures.
The observational studies, using hard X-rays (HXRs) observed by the RHESSI mission,
concentrate on four flares, which support the classical magnetic reconnection model of
solar flares in various ways.
In the X3.9 flare occurring on 11/03/2003, there is a monotonic upward motion of the loop
top (LT) source accompanied by a systematic increase in the separation of the footpoint (FP)
sources at a comparable speed. This is consistent with the reconnection model
with an inverted-Y geometry.
The 04/30/2002 event exhibits rarely observed two coronal sources.
The two sources (with almost identical spectra) show energy-dependent structures,
with higher-energy emission being close together.
This suggests that reconnection takes place within the region between the sources.
In the 10/29/2003 X10 flare, the logarithmic total HXR flux of the FPs
correlates with the mean magnetic field. The two FPs
show asymmetric HXR fluxes, which is qualitatively consistent with the magnetic mirroring effect.
The M1.7 flare on 11/13/2003 reveals evidence of evaporation directly imaged by RHESSI for
the first time, in which emission from the legs of the loop appears at intermediate energies.
The emission centroid moves toward the LT as time proceeds, indicating an increase of density in the loop.
The theoretical modeling of this work combines the stochastic acceleration model with the NRL hydrodynamic
model to study the interplay of the particle acceleration, transport, and radiation
effects and the atmospheric response to the energy deposition by nonthermal electrons.
We find that low-energy electrons in the quasi-thermal portion of the spectrum
affects the hydrodynamics by producing more heating in the corona than the previous models
that used a power-law spectrum with a low-energy cutoff.
The Neupert effect is found to be present and effects of suppression of conduction are
tested in the presence of hydrodynamic flows.
Authors: Wei Liu (Adviser: Vahé Petrosian)
Publication Status: 2006, Ph.D. Thesis, Stanford University (10 chapters, 224 pages)
Last Modified: 2006-12-21 09:54