SOLAR RADIO MICROBURSTS AT 1.4 GHZ

The Very Large Array was used for a period of almost-equal-to 80 minutes on 1989 September 11 to observe the Sun at two frequencies in the 1.4 GHz band. In addition to a strong radio burst (700 sfu at maximum) of a duration of roughly 15 minutes, a multitude of small-amplitude, transient bursts occurred during the course of the observation. Specifically, some tens of microbursts occurred during a period of 65 minutes, ranging in amplitude from less-than-or-similar-to 0.05 to 4 sfu, and ranging in duration from < 10 to 40 s. A sample of these microbursts studied in detail shows that they occurred at five distinct locations in four different active regions. The microbursts are probably due to plasma radiation although the microburst mechanism remains unknown. Their relation to known radio burst phenomena and hard X-ray microflares is unclear.