An extensive study of the IMP-6 and IMP-8 plasma and radio wave data has been performed to try to find electron plasma oscillations associated with type III radio noise bursts and low energy solar electrons. This study shows that electron plasma oscillations are seldom observed in association with solar electron events and type III radio bursts at 1.0 AU. In nearly four years of observations only one event was found in which electron plasma oscillations are clearly associated with solar electrons. Numerous cases were found in which no electron plasma oscillations with field strengths greater than 1 /xV/m could be detected even though electrons from the solar flare were clearly detected at the spacecraft.
For the one case in which electron plasma oscillations are definitely produced by the electrons ejected by the solar flare, the electric field strength is very small, only about 100/xV/m. This field strength is about a factor of ten smaller than the amplitude of electron plasma oscillations generated by electrons streaming into the solar wind from the bow shock. Electromagnetic radiation, believed to be similar to the type III radio emission, is also observed coming from the region of more intense electron plasma oscillations upstream of the bow shock. Quantitative calculations of the rate of conversion of the plasma oscillation energy to electromagnetic radiation are presented for plasma oscillations excited by both solar electrons and electrons from the bow shock. These calculations show that neither the type III radio emissions nor the radiation from upstream of the bow shock can be adequately explained by a current theory for the coupling of electron plasma oscillations to electromagnetic radiation. Possible ways of resolving these difficulties are discussed. Full text can be found in the paper 'Electron Plasma Oscillations Associated with Type III Radio Emissions and Solar Electrons', Solar Physics 45 (1975), 477. Discussion D. Smith: Electron anisotropy in the April 6, 1971 event could give enhanced emission.
Gurnett:
The event did have a pronounced anisotropy. Steinberg: The plasma oscillations could be localized, but the radio and electron observations indicate large sources.
Gurnett: On IMP-6, the time resolution is approximately ~o s. Plasma oscillations occur in about 1 out of 30 type III bursts. We have 3 cases which we think are not magnetosheath.
Melrose:
We do not know the solar wind scale length. The emission could be uniform at the second harmonic but the plasma waves could be localized.
R. Smith:
What is the effective antenna length? Gurnett: Effective length = 89 physical length. Dunckel: Your observations show the bow shock emissions traveled through magnetosheath. Might the 2wp waves be absorbed? Kellogg: Density enhancement in magnetosheath is generally less than 4, so the 2wp waves will be transmitted.