34th Solar Physics Division Meeting, June 2003
Session 15 Flares and Microflares I
Oral, Wednesday, June 18, 2003, 1:30-3:30pm, Auditorium

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[15.05] Spectral Dynamics of Solar Broadband Microwave Bursts.

V. F. Melnikov, D. E. Gary, G. Nita (CSTR/NJIT)

Microwave spectral observations provide important information on acceleration and transport of mildly relativistic electrons as well as on magnetoactive plasma in solar flaring loops. In this study we analyze dynamics of the frequency spectrum of a sample of broad band microwave bursts selected to have only a single spectral maximum and simple time profiles, using data obtained in 2001 with the OVSA solar-dedicated frequency-agile interferometer. In particular, we study the evolution during a burst of such parameters as the spectral peak frequency fp, the ratio of fluxes at f > fp and f < fp, the average spectral indices above and below fp, as well as the frequency distribution of local spectral indices.

The most common dynamic properties of the parameters are as follows. Peak frequency changes with time, increasing on the rising phase and decreasing on the decay phase of bursts. The ratio of fluxes at f > fp and f < fp in most of cases increases on the rise phase and decreases on the decay phase. Spectral indices above and below fp decrease their absolute value on the decay phase. However this general time behavior may change to opposite one in some events.

The spectral peculiarities found are then compared with relevant theoretical expectations derived from model simulations of radio emission that take into account some effects of energetic electron spectral and spatial evolution in flaring loops and also their pitch-angle anisotropy. We also consider the influence of self-absorption and dense plasma inside the loop (Razin effect) on the spectral characteristics of the gyrosynchrotron emission. Finally, results of the comparisons are used to get new information on the high energy electron kinematics and temporal evolution of plasma parameters inside flaring loops.

This work is supported by NASA grants NAG5-10212 and NAG5-10891. OVSA/NJIT is supported by NSF under grant AST-9987366.


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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.