Physics – Plasma Physics
Scientific paper
Oct 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001jgr...10621701s&link_type=abstract
Journal of Geophysical Research, Volume 106, Issue A10, p. 21701-21717
Physics
Plasma Physics
12
Interplanetary Physics: Solar Wind Plasma, Interplanetary Physics: Instruments And Techniques, Ionosphere: Plasma Temperature And Density, Space Plasma Physics: Spacecraft Sheaths, Wakes, Charging
Scientific paper
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.
Bosqued Jean Michel
Bougeret Jean-Louis
Larson Davin E.
Lin Robert P.
Maksimovic Milan
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