Abstract
A study is made of the initial stage of the 25 August 1999, event using high time-resolution microwave observations, as well as the data from the Siberian Solar Radio Telescope and Yohkoh/SXT/HXT. Microwave emission revealed fine structures with a typical time scale of about 1 s with a frequency drift ∼1 GHz/s, and structures with a typical time scale of less than 0.1 s with a frequency drift ∼10 GHz/s. Emission bands with a slower frequency drift are generated by energetic electrons subjected to the cyclotron resonance condition. This slower frequency drift is a consequence of a change in plasma density caused by the coalescence of magnetic structures with a typical size of the order of ∼10 8 cm, while the emission with a faster drift is generated by beams of energetic electrons generating Cherenkov resonance emission. The energetic electron beams are produced as a result of the interaction of magnetic structures ∼10 6–10 7 cm in size.
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