A group of solar microwave type III bursts with reversed drift rates on Nov 4, 1997

The most important feature of the microwave type III bursts on Nov. 4, 1997 is the periodically reversed drift rates, which may be contributed to a gr oup of electron beams trapped by a huge magnetic tube (10(4) km). It is sug gested that these electron beams are accelerated by the same mechanism, bec ause there is a power law distribution with index 3.2 in the energetic spec trum of the beam. On the other hand, the energy release in each pulse is qu asi-quantized, which is confirmed by the statistical correlation between th e rising time and the burst flux. Both of these two results are based on th e model of plasma instability responsible for the burst.