C. de Villedary

ULF waves in the Io torus: Ulysses observations

Throughout the Io torus, Ulysses has observed intense ultralow frequency (ULF) wave activity in both electric and magnetic components. Such ULF waves have been previously suggested as the source of ion precipitation leading to Jovian aurorae. The peaks of the wave spectra are closely related to the ion cyclotron frequencies, which is evidence of the waves being ion cyclotron waves (ICWs). Analysis of the dispersion relation using a multicomponent density model shows that at high latitudes (approximately 30 deg), peak frequencies of the waves fall into L mode branches of guided or unguided ICWs. Near the equator, in addition to the ICWs below f cO(2+) , there are strong signals at approximately 10 Hz which require an unexpectedly large energetic ion temperature anistropy to be explained by the excitation of either convective or nonconvective ion cyclotron instabilities. Their generation mechanism remains open for the future study. Evaluation of the Poynting vector and the dispersion relation analysis suggest that the waves near the equator had a small wave angle relative to the magnetic field, while those observed at high latitudes were more oblique. The polarization of the waves below f cH(+) is more random than that of the whistler mode waves, but left-hand-polarized components of the waves can still be seen. The intensity of the ICWs both near the equator and at high latitudes are strong enough to meet the requirement for producing strong pitch angle scattering of energetic ions.

Observations of electron plasma waves upstream of the Jovian bow shock

Abstract The Ulysses spacecraft encountered the planet Jupiter in February 1992, on its journey towards high heliospheric latitude. During the approach to the planet, as well as on the outbound pass, while receding from the Jovian bow shock, the Plasma Frequency Receiver that is part of the Unified Radio and Plasma Wave experiment (URAP) recorded bursts of plasma waves in the frequency range of a few kHz. These emissions, first observed by the PWS experiment onboard the Voyager spacecraft, have been identified as upstream electron plasma waves. In this paper, we present the first analysis of the characteristics of these emissions, which are very similar to those found in the Earths electron foreshock, upstream of the Earths bow shock. These bursty emissions, with a peak frequency very close to the local electron plasma frequency Fpe, have a typical electric field amplitude in the range 0.01–0.1 mV m−1, with some bursts above 1 mV m−1. The frequency bandwidth over which significant power can be found above the instrument background noise ranges from below 0.2 Fpc to about 2 Fpc. On the basis of our present knowledge of similar emissions observed at Earth, we suggest that the broadband emissions are triggered by suprathermal (a few tens of eV) electrons, streaming back from Jupiters bow shock.

Correlation between terrestrial myriametric and kilometric radio bursts observed with Galileo

Data from the Galileo plasma wave system recorded during an investigation of the Earth magnetotail on December 8, 1990, are analyzed in both the myriametric and the kilometric wavelength range. In the far tail, between 80 and 30 Earth radii, two components are observed in the myriametric range (frequencies between 6 and about 30 kHz): (1) the “classical” trapped continuum radiation with a smoothly varying intensity in time and (2), superposed on this component, bursts of waves with typical spectral densities of 10−15 V²m−2Hz−1. These bursts of myriametric waves are shown B to correlate with bursts of intense auroral kilometric radiation (AKR) with typical spectral density of 10−12 V²m−2Hz−1. This bursty myriametric radiation is the analog of the low frequency radiation (LFR) reported by Filbert and Kellog (1989). Its close correlation with the kilometric radiation suggests the existence of a direct relationship between these two radiations. A generation mechanism that explains this correlation and the frequency gap between the AKR and the LFR is proposed.