太阳物理研究组知识库

A total of 266 type III bursts observed with the 2.6 - 3.8 GHz high temporal resolution dynamic spectrometer of NAOC during the 23rd solar cycle (from April in 1998 to January III 2003) are statistically analyzed in this present paper. The frequeucy drift rates (normal and reverse slop), durations, polarizations, bandwidth, starting and ending frequencies are analyzed in detail. From the statistical results of starting and ending frequencies we show that the re-ions of starting frequencies are very large, which are from less than 2.6 GHz to greater than 3.8 GHz; but the ending frequencies regions are relative concentration, which are from 2.82 GHz to 3.76 GHz. These phenomena mean that the sites of electrons acceleration are quite scatter, while the cutoff regions of the radio type III bursts are in the limiting domain. The bursts number with positive and negative drift rates are nearly equal. This correlation may interpret the suggest that a proportional number of electron beams in the directions of upward and downward are accelerated in the range of 2.6 - 3.8 GHz. The other statistical results are similar to those of decimetric type III bursts as statistics in previous literature. The emission mechanisms of microwave type III bursts are mainly caused by the plasma radiation and electron gyro-maser radiation. From the statistics of microwave type III bursts and associated coronal mass ejections (CMEs), it is found that the 36% of type III bursts (97) are corresponding to the CMEs for occurring time and site. The correlation between the type III bursts and CMEs is not close, and most type III bursts are occurred in the time regions of 26 - 30 minutes before CMEs. This means that the partial microwave type III bursts may be a precursor of the CMEs.