Type III solar noise observed below 100 kHz on OGO 3

Abstract

Type III solar noise bursts have been observed in the frequency range 25-100 kHz with the VLF detector on OGO 3. The bursts decrease in frequency from 100 kHz (the highest frequency of observation) to as low as 25 kHz in approximately 45 min. The intensity at 100 kHz increases for about 20 min then decays over a period of approximately 1 h. The variation of the intensity with time becomes less regular at lower frequencies. Observed maximum intensities near 80 kHz range from 3 • 10 -I8 to 2 • 10 -16 W m -~ Hz -1. Bursts are predominantly associated with west-limb flares. Their commencement at 100 kHz tends to follow type III bursts observed at 2-4 MHz by about 10 min. Observed drift rates and decay times correspond roughly to those extrapolated from higher frequency measurements. Type III and the so-called 'high-pass' noise bursts often occur simultaneously, presenting a problem in identification. The solar noise events can be distinguished by their relatively slow time variation, smooth spectrum, and low intensity.

40. Radio Astronomy

“…On hectometric wavelengths, type-Ill burst storms have been observed (78), in association with metric and decametric activity (79). These observations were extended down to 30 KHz (80) (81). Physical conditions and evidence for spiral structure were deduced (82).…”