A new class of kilometer wavelength solar radio bursts has been observed with the ISEE‐3 Radio Astronomy Experiment. These events resemble groups of ordinary type III bursts but have some unique properties. They are very intense and have durations considerably longer than groups of type III bursts. The new class of events do not necessarily occur at the times of reported meter wavelength type III activity and therefore do not appear to be the continuation of such activity to long wavelengths. Instead they occur at the reported times of type II events, which are indicative of a shock wave. An examination of records from the Culgoora Radio Observatory shows that the associated type II bursts have fast drift elements emanating from them i.e. herringbone structure. It is proposed that the new class of bursts are the long wavelength continuation of herringbone structure and it seems probable that the electrons producing the radio emission are accelerated by shocks. The new type of events will be referred to as shock accelerated (SA) events. The characteristics of SA events are discussed.

The noise voltage found at the terminals of an electric dipole antenna immersed in a hot plasma is calculated. The plasma is assumed stable and at rest. It is described as made of two maxwellian electron populations. A grid of calculated noise spectra is presented in normalized coordinates, and we give analytical expressions valid for frequencies much lower or larger than the plasma frequency f•, or close to the noise peak. The antenna impedance is also calculated; in contrast to the noise spectrum, it is found to be very weakly dependent upon the hot population parameters. From these results one can calculate the response of a receiving system, thus enabling the actual measurement of the plasma parameters from the noise spectrum. Using ISEE 3 SBH experimental data, it is shown that the observations do fit the theoretical predictions over most of the frequency range. Plasma parameters are obtained and found in good agreement with results from the Los Alamos plasma analyzer on the same spacecraft. It appears that the high energy tail of the particle distribution function accounts for the peak noise voltages of several times 10 -12 V2Hz -1 found at the terminals of a 45-m half-length dipole. The interpretation of these observations does not therefore require an unstable plasma. We discuss these results and show that more work should be done to explain an unpredicted increase of the spectrum below f•, and to explain the weak spin modulation. Solving these remaining problems requires the introduction of ions and of the bulk and/or drift velocity into the calculations. Appendix A contains a partial justification of the assumption of a triangular current distribution on the antenna. The calculations are presented in appendix B. Za = R -iX = d3r ß E(r)-J(r) (1) ß 10 2 where E(r) is the field of the harmonic source J(r) in the plasma which satisfies in k space (spatial Fourier transform): 11,127 11,128 COUTURIER ET AL.: QUASI-THERMAL PLASMA NOISE COUTURIER ET AL.' QUASI-THERMAL PLASMA NOISE 11,129The Array of Spectra When the plasma is in thermal equilibrium, Nyquist theorem can be used, and the spectra are obtained from the variation of the radiation resistance in the longitudinal mode, Rr, with f/fp (Figure 1). Of course we obtain the same results as Kuehl [1967], but, to get more practical usefulness, we calculated more Rr curves than he did. At frequencies lower than ft,, the noise spectrum is flat. There is a cutoff at fife = 1, followed, on the high frequency side, by a noise peak which becomes higher, narrower, and closer to ft, for larger values of l/lo. This simply corresponds to the fact that the antenna has a peak response to plasma waves whose wavelength is of order I. When l/lo increases, this peak wavelength increases, the corresponding plasma wave frequency tends to ft,, and the received bandwidth becomes narrower. This is a direct consequence of the plasma wave dispersion relation, which can be approximated by f---fe (1 + 3 klo) 1/2 forf-• ft,. At frequencies larger than about 3-5 ft, and for any l/lo > 1...

INAbstract. Fifteen type II solar radio events have been identified in the 2 MHz to 30 kHz frequency range by the radio astronomy experiment on the ISEE-3 satellite over the period from September 1978 to December 1979. These data provide the most comprehensive sample of type II radio bursts hitherto observed at kilometer wavelengths. Dynamic spectra of a number of events are presented. Where possible, the 15 events have been associated with an initiating flare, ground-based radio data, the passage of a shock at the spacecraft and the sudden commencement of a geomagnetic storm. The general characteristics of kilometric type II bursts are discussed.

Narrow band radio emissions are observed with the radio astronomy experiment on ISEE 3 from a position 0.01 AU upstream of the earth. These are interpreted as radio line emission generated at twice the local plasma frequency in the vicinity of the earth's bow shock by energetic particles. The frequency of the 2fp radio emission is well correlated to large scale density changes observed by both the LASL plasma experiment and the radio experiment at ISEE 3, about one hour earlier in accordance with the transit time of the solar wind to the bow shock region. The bandwidth of the 2fp emission varies from less than 3 kHz to more than 20 kHz and is likely broadened by solar wind density variations across the source region. The 2fp source is visible about 50% of the time and the position of its centroid is usually located within 30 RE of the subsolar point, but at times is observed at a distance of up to 60 RE. However, these positions may have systematic errors if significant linear polarization is present in the observed radiation or if refraction takes place along the ray path. Intensity variations of 20 db and apparent motions of 40 RE can occur with time scales of minutes.

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