Time scales of the slowly drifting pulsating structure observed during the April 12, 2001 flare

Abstract

First time scales of high-frequency (500-1500 MHz) slowly drifting pulsating structures observed during the April 12, 2001 flare by the Ondřejov (800-4500 MHz) and Potsdam (40-800 MHz) radiospectrographs and by the 1420 and 610 MHz Trieste radiopolarimeters (with high time resolution (1 ms)) are studied statistically. The Fourier method reveals periods in the range of 0.9-7.5 s. For shorter periods the power spectra show a power-law form, especially in the interval of about 0.06-0.2 s, where the power-law index is in the 1.3-1.6 range. The results are interpreted using the flare model with plasmoid ejections. For the first time, the multi-scale cascading reconnection process is included in the interpretation. Corresponding time scales are estimated analytically. Further, magnetic reconnection in the bursting regime is simulated in a 2-D MHD model and variations of the dissipation power and radio radiation measure are computed. Fourier spectra of these numerical variations are determined and compared with those obtained from observations.