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Ann. Geophys., 20, 609-618, 2002
www.ann-geophys.net/20/609/2002/
© European Geosciences Union 2002
Evidence for the interplanetary electric potential? WIND observations of electrostatic fluctuations
C. Lacombe1, C. Salem2, A. Mangeney1, D. Hubert1, C. Perche1, J.-L. Bougeret1, P. J. Kellogg3, and J.-M. Bosqued4
1DESPA/CNRS, Observatoire de Paris, 92195 Meudon, France
2Space Science Laboratory, University of California, Berkeley, CA 94720, USA
3School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55454, USA
4CESR/CNRS, Université Paul Sabatier, BP 4346, 31029 Toulouse, France
Correspondence to: C. Lacombe
(clacombe@despace.obspm.fr)
Abstract. In the solar wind at 1
AU, coherent electrostatic waveforms in the ion acoustic frequency range (~
1 kHz) have been observed by the Time Domain Sampler (TDS) instrument on the
Wind spacecraft. Small drops of electrostatic potential (Df
> 10-3 V) have been found across some of these
waveforms, which can thus be considered as weak double layers (Mangeney et al.,
1999). The rate of occurrence of these potential drops, at 1 AU, is estimated
by a comparison of the TDS data with simultaneous data of another Wind
instrument, the Thermal Noise Receiver (TNR), which measures continuously the
thermal and non-thermal electric spectra above 4 kHz. We assume that the
potential drops have a constant amplitude and a constant rate of occurrence
between the Sun and the Earth. The total potential drop between the Sun and the
Earth, which results from a succession of small potential drops during the
Sun-Earth travel time, is then found to be about 300 V to 1000 V, of the same
order of magnitude as the interplanetary potential implied by a two-fluid or an
exospheric model of the solar wind: the interplanetary potential may manifest
itself as a succession of weak double layers. We also find that the hourly
average of the energy of the non-thermal ion acoustic waves, observed on TNR
between 4 and 6 kHz, is correlated to the interplanetary electrostatic field,
parallel to the spiral magnetic field, calculated with a two-fluid model: this
is another evidence of a relation between the interplanetary electrostatic
field and the electrostatic fluctuations in the ion acoustic range. We have yet
to discuss the role of the Doppler effect, which is strong for ion acoustic
waves in the solar wind, and which can bias the measure of the ion acoustic
wave energy in the narrow band 4–6 kHz.
Key words. Interplanetary physics
(plasma waves and turbulence; solar wind plasma) Space plasma physics
(electro-static structures)
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