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

First time scales of high-frequency (500-1500 MHz) slowly drifting pulsating structures observed during the April 12, 2001 flare by the Ond. rejov (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.