A. Mangeney

Determination of accurate solar wind electron parameters using particle detectors and radio wave receivers

We present a new, simple, and semiempirical method for determining accurate solar wind electron macroscopic parameters from the raw electron moments obtained from measured electron distribution functions. In the solar wind these measurements are affected by (1) photoelectrons produced by the spacecraft illumination, (2) spacecraft charging, and (3) the incomplete sampling of the electron distribution due to a nonzero low-energy threshold of the energy sweeping in the electron spectrometer. Correcting fully for these effects is difficult, especially without the help of data from other experiments that can be taken as a reference. We take here advantage of the fact that high-resolution solar wind electron parameters are obtained on board Wind using two different instruments: the electron electrostatic analyzer of the three-dimensional Plasma experiment (3DP), which provides 3-D electron velocity distribution functions every 99 s as well as 3-s resolution computed onboard moments, and the thermal noise receiver (TNR), which yields unbiased electron density and temperature every 4.5 s from the spectroscopy of the quasi-thermal noise around the electron plasma frequency. The present correction method is based on a simplified model evaluating the electron density and temperature as measured by the electron spectrometer, by taking into account both the spacecraft charging and the low-energy cutoff effects: approximating the solar wind electron distributions by an isotropic Maxwellian, we derive simple analytical relations for the measured electron moments as functions of the real ones. These relations reproduce the qualitative behavior of the variation of the raw 3DP electron density and temperature as a function of the TNR ones. In order to set up a precise “scalar correction” of the raw 3DP electron moments, we use the TNR densities and temperatures as good estimates of the real ones; the coefficients appearing in the analytical relations are obtained by a best fit to the data from both instruments during a limited period of time, chosen as a reference. This set of coefficients is then used as long as the mode of operation of the electron spectrometer is unchanged. We show that this simple scalar correction of the electron density and temperature is reliable and can be applied routinely to the high-resolution 3DP low-order moments. As a by-product, an estimate of the spacecraft potential is obtained. The odd-order moments of the distribution function (electron bulk speed and heat flux) cannot be corrected by the model since the distribution is assumed to be an isotropic Maxwellian. We show, however, that a better estimate of the electron heat flux can be obtained by replacing the electron velocity by the proton velocity.

Early results from the ISEE electron density experiment

The ISEE-1 and 2 spacecraft contain two complementary experiments to measure the ambient electron density by radio techniques: a propagation experiment which measures the integrated electron density between ISEE-1 and 2, and a resonance sounder which measures the electron density in the vicinity of ISEE-1, and also provides AC electric field data. These experiments have been described elsewhere (Harvey et al., 1978). Results from these two experiments are presented here for the first time. The propagation experiment permits high time resolution studies of density fluctuations in the solar wind and magnetospheric frontier regions. The sounder experiment has detected for the first time plasma resonances in the solar wind and in the Earths magnetosheath, as well as in the regions of the magnetosphere where resonances have already been observed by the spacecraft GEOS-1. We present here a preliminary review of the different types of electric field noise observed in the solar wind and magnetosheath, and discuss their relationship to the measured plasma density.

Solar wind thermal electrons in the ecliptic plane between 1 and 4 AU - Preliminary results from the Ulysses radio receiver

The radio receiver of the Unified Radio and Plasma (URAP) experiment aboard the Ulysses spacecraft records spectra of the quasi-thermal plasma noise. The interpretation of these spectra allows the determination of the total electron density Ne and of the cold (core) electron temperature Tc in the solar wind. A single power law does not fit the variations of Ne which result from the contribution from different solar wind structures. The distribution of the values of Tc suggests that, on the average, the solar wind is nearly isothermal.

Interplanetary fast shock diagnosis with the radio receiver on Ulysses

ABSTRACT The Radio receiver on Ulysses records the quasi-thermal noise which allows a determination of the density and temperature of the cold (core) electrons of the solar wind. Seven interplanetary fast forward or reverse shocks are identified from the density and temperature profiles, together with the magnetic field profile from the Magnetometer experiment. Upstream of the three strongest shocks, bursts of non-thermal waves are observed at the electron plasma frequency f peu. The more perpendicular the shock, the longer is the time interval during which these upstream bursts are observed. For one of the strongest shocks we also observe two kinds of upstream electromagnetic radiation: radiation at 2 f peu , and radiation at the downstream electron plasma frequency, which propagates into the less dense upstream regions.

Observations of nonlinear turbulence in the upstream solar wind

SummaryPlasma, electric-field and magnetic-field data from several experiments on board the spacecraft ISEE 1 and 2 have been analysed in the interaction region upstream of the Earths bow shock. Upstream waves which are known to be associated with diffuse distributions of backstreaming protons are shown to correlate also with variability in the distribution of the incoming solar-wind protons. Both phenomena are also clearly connected with the presence of enhanced electric-field turbulence. On the basis of these relations, a preliminary discussion can be given of the complex nonlinear plasma processes occurring in the foreshock region.

Density and field structure of a FTE observed in the magnetosphere

ISEE1 and 2 high resolution electron density and magnetic field measurements have been used to study characteristic structures, identified as FTEs, observed inside the magnetosphere close to the magnetopause. We investigate new properties: a volcano-like signature in the magnetic field strength, a thin sheet structure at the leading edge, and a wake. The plasma compressibility is analysed through the structure. Auto and cross spectral analysis of the data reveal the signature of compressive modes in the wake of the FTE.

PLASMA WAVE PHENOMENA AT INTERPLANETARY SHOCKS OBSERVED BY THE ULYSSES URAP EXPERIMENT

We present Ulysses URAP observations of plasma waves at seven interplanetary shocks detected between approximately 1 and 3 AU. The URAP data allows ready correlation of wave phenomena from .1 Hz to 1 MHz. Wave phenomena observed in the shock vicinity include abrupt changes in the quasi-thermal noise continuum, Langmuir wave activity, ion acoustic noise, whistler waves and low frequency electrostatic waves. We focus on the forward/reverse shock pair of May 27, 1991 to demonstrate the characteristics of the URAP data.

Some Basic Aspects of Solar Wind Acceleration

We discuss some effects related to particle coherent orbits in the acceleration region and in the wind. (1) In the distant wind, when collisions are negligible, the temperature of escaping electrons follows adiabatic anisotropic (CGL) relations, whereas those reflected by the electrostatic and/or mirror forces behave as an adiabatic isotropic fluid; hence, contrary to a widespread view, electrons do not follow a single adiabatic law in absence of collisions. (2) In the corona, if one superimposes a minute hot maxwellian tail to a maxwellian velocity distribution, the relative importance of the tail increases rapidly with height; this is fundamentally different from a Kappa distribution, whose non maxwellian character remains constant with height. Suprathermal electrons also produce a large heat flux because many of them escape from the electric potential. (3) Fluid models, exospheric models, and a numerical simulation including particle orbits and collisions agree on finding that when an accelerated trans...