MICROWAVE TYPE III-RS BURSTS

A decimetric( 1600 +/- 100 MHz), high-sensitivity digital spectroscope has been put into regular operation at Sao Jose dos Campos, Brazil, s ince 1991 March. The dynamic spectra are recorded on 35 mm film while 20 frequencies each separated by 10 MHz are digitized with time resolu tion of 100 ms. So far, about 350 groups of solar bursts have been obs erved by this system. These have been classified as microwave type and decimetric reverse slope (RS) type III bursts. Here, we report statis tical investigations of the properties of the 44 moderately strong gro ups of decimetric type III-RS bursts. The average total duration of th ese bursts is similar to 0.7 s, the drift rate varied between similar to 400 and 3000 MHz s(-1), and average decay time is similar to 120 ms . These observed drifts and timescales suggest that decimetric type II I-RS bursts are generated by beam plasma interaction at second harmoni c in the inhomogeneous chromosphere, and that the acceleration region is located at a density level of less than or equal to 10(9) cm(-3).