An exploration of the origin of bidirectional electron beams in the solar corona with observations of pairs of type III radio bursts

Three paired type III radio bursts from metric to microwave regions observe d with radio spectrometers at Yunnan and Bejing Observatories are investiga ted. The frequencies and heights of bidirectional electron beams are estima ted. The normal and reverse drifts in the three events separate at three ve ry different frequencies of 250, 1300 and 2900 MHz, but each within a narro w range between 4 and 100 MHz. Compact acceleration sources are indicated w here originate both upward and downward moving electron beams. The magnetic structure topology, the size of the source of electron acceleration, the v elocity of the electron beams and the mechanism of paired type III bursts a re discussed.