Study of solar microwave radiation using multifrequency data

Citation

Lee, Jeongwoo (1994) Study of solar microwave radiation using multifrequency data. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/1vr9-wh15. https://resolver.caltech.edu/CaltechETD:etd-09102008-092806

Abstract

I have carried out analysis of multifrequency data of solar microwave radiation gathered by the frequency-agile telescope at Owens Valley Radio Observatory to address several long-standing problems in the study of active region structure and solar flare particles. In the study of active region structure, I use the microwave data and the magnetograms of NOAA 4741 obtained during 1986 August 2 - 9 to discover: (i) change of dominant radiation mechanism with the coronal height, (ii) angle-dependent properties of the gyroresonance opacity, (iii) distribution of the coronal magnetic fields and its implication for the force balance in the upper atmosphere of the active region. The merit of this study lies in the fact that most results are empirical and thus provide an observational basis to test theoretical sunspot models and the gyromagnetic radiation theory. In the flare study, I deal with impulsive bursts and extended bursts, aiming at two issues: (i) the physical link between microwaves and hard X-rays in impulsive bursts and (ii) influence of ambient plasma on the evolution of extended microwave activity. The first issue has been addressed by a kinetic approach made to deduce the distribution of microwave-emitting electrons and hard X-ray electrons in momentum space, referring to the 1989 March 18 flare in NOAA 5395. For the second issue, I analyse data of extended microwave bursts on 1990 May 24 (NOAA 6063), 1991 March 7 and 8 (NOAA 6538), and 1991 March 22 (NOAA 6555) in terms of a nonuniform coronal trap model to deduce source conditions responsible for the observed anomalies of extended bursts. These data sets and results of analysis underline the influence of the source condition on the spectral and temporal evolution of microwave radiation during solar flares.

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