Acceleration of Bidirectional Eletron Beams in Corona

The metric and microwave spike emission with negative and positive frequency drift rate observed with radio spectrometers at Yunnan and Beijing observatories are presented. The frequencies and heights at which the bidirectional electron beams originated are estimated. Two events reveal a separatrix frequency(at 250 and 2900 MHz) between normal-and reverse-drifting radio bursts, indicating a compact acceleration source where electron beams are injected in both the upward and downward directions. There cases may indicate that the change over frequencies of bidirectional electron beams are within a large band from 250 to 2900 MHz and the originating(frequency bands of separatrix) are in a very small(4 to 100 MHz) and different bands. The type Ⅲ bursts appear to be a plasma emission phenomenon from a beam of electrons which seem to have widely separated acceleration regions from the high to low corona. These cases suggests that current sheets that separate open and closed magnetic fluxes in the low corona, and oppositely directed open field lines in the high corona are possible sites for bidirectional electron acceleration. The regions of magnetic topology from closed to open magnetic field structures should be very large(about from 2×10⁴km to 10.7×10⁴km above the photosphere).