Some characteristics of dynamic spectra of solar bursts

Extract

The sun has been observed daily at the University of Michigan during the last year with three sweep-frequency receivers covering the 100 to 580 Mc/s band three times a second. The output is displayed as an intensity-modulated line on a precision cathode-ray tube that is photographed on a 35-mm film moving about one centimeter per minute, thereby producing a frequency-time record with solar intensities recorded as variations in photographic density. The combination of the film characteristic and the logarithmic response of the IF amplifier permits the recording of a wide range of intensities in greater detail than before. A number of typical radio events associated with solar flares have been obtained; a typical sequence is a short group of intense type III bursts (fast drifts) followed within minutes by a type II burst (slow drifts) lasting 10 to 30 minutes, and followed by a type I noise storm, with or without a continuum increase, continuing for hours or days. The type I event is usually confined to frequencies below about 200 Mc/s, whereas the type III and type II (bursts) have been recorded up to 580 Mc/s.