The analysis of type III bursts observed from the OGO-5 satellite between 3.5 MHz and 50 kHz (46 km) gives an empirical expression for the frequency drift rate as a function of frequency that is valid from 75 kHz to 550 MHz. Using this expression and some simplifying assumptions we obtain indirectly an empirical formula for the electron density distribution of the solar wind to 1 AU which is consistent with published values of electron density and with observed type II1 burst drift rates.
Type llI bursts were observed between 3.5 MHz and 50 kHz by the University of Michigan radio astronomy experiment aboard the OGO-5 satellite.Decay times were measured and then combined with published data ranging up to about 200 MHz. The observed decay times increase with decreasing frequency but at a rate considerably slower than that expected from electron-proton Coulomb collisions. At 50 kHz values differ by about a factor of 100. Using Hartle and Sturrock's solar wind model, Coulomb collisional frequencies were computed and compared with the apparent collisional frequencies deduced from the observations. It was found that the ratio of observed to computed values varies with heliocentric distance according to an inverse 0.71 power. This is similar to an ad hoc function used by Wolff, Brandt, and Southwick to increase the electron-proton collisional energy exchange and make the solar wind theory agree with the measurements of electron and proton temperature near the Earth. These results may provide a clue about the nature of the non-collisional plasma wave damping process responsible for the short duration of type III bursts.
Type III radio bursts observed at kilometric wavelengths (~< 0.35 MHz) by the OGO-5 spacecraft are compared with > 45 keV solar electron events observed near I AU by the IMP-5 and Explorer 35 spacecraft for the period March 1968-November 1969 Fifty-six distinct type lI[ bursts extending to ~< 0.35 MHz (> 50 R| equivalent height above the photosphere) were observed above the threshold of the OGO-5 detector; all but two were associated with solar flares. Twenty-six of the bursts were followed ~< 40 min later by > 45 keV solar electron events observed at 1 AU. All of these 26 bursts were identified with flares located west of W09 solar longitude. Of the bursts not associated with electron events only three were identified with flares west of W09, 18 were located east of W09 and 7 occurred during times when electron events would be obscured by high background particle fluxes.Thus almost all type [II bursts from the western half of the solar disk observed by OGO-5 above a detection flux density threshold of the order of 10 -la Wm -z Hz -1 at 0.35 MHz are followed by > 45 keV electrons at 1 AU with a maximum flux of ~> 10 cm -z s -1 ster -1. If particle propagation effects are taken into account it is possible to account for lack of electron events with the type III bursts from flares east of the central meridian. We conclude that streams of ~ 10-100 keV electrons are the exciting agent for type III bursts and that these same electrons escape into the interplanetary medium where they are observed at 1 AU. The total number of > 45 keV electrons emitted in association with a strong kilometer wavelength type III burst is estimated to be >I 5 • 10 a2.
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