HR: 10:50h
AN: SM12B-03    [Abstracts]
TI: Electron density estimation in the magnetotail: a multi-instruments approach
AU: * Masson, A
EM: Arnaud.Masson@esa.int
AF: Research and Scientific Support Department, European Space Agency, ESTEC, Kepleraan 1, Noordwijk, 2201AZ, Netherlands
AU: Taylor, M
AF: Research and Scientific Support Department, European Space Agency, ESTEC, Kepleraan 1, Noordwijk, 2201AZ, Netherlands
AU: Escoubet, C
AF: Research and Scientific Support Department, European Space Agency, ESTEC, Kepleraan 1, Noordwijk, 2201AZ, Netherlands
AU: Fazakerley, A
AF: MSSL, Mullard Space Science Laboratory, University College London, Dorking, RH5 6NT, United Kingdom
AU: Trotignon, J
AF: LPCE, CNRS and Université d'Orléans, 3A, avenue de la recherche scientifique, Orléans, 45071, France
AU: Décreau, P
AF: LPCE, CNRS and Université d'Orléans, 3A, avenue de la recherche scientifique, Orléans, 45071, France
AU: {Å}snes, A
AF: Research and Scientific Support Department, European Space Agency, ESTEC, Kepleraan 1, Noordwijk, 2201AZ, Netherlands
AU: Santol\'ik, O
AF: Faculty of Mathematics and Physics, Charles University, V Holesovickach 2, Praha 8, Prague, CZ-18000, Czech Republic
AU: Laakso, H
AF: Research and Scientific Support Department, European Space Agency, ESTEC, Kepleraan 1, Noordwijk, 2201AZ, Netherlands
AB: { } An accurate in-situ estimation of the electron density in the Earth^'s magnetotail is needed to understand key geophysical phenomena at different scales: from the microphysics of magnetic reconnection to large-scale phenomena studied using three dimensional (3D) mapping of the electron density.
{ } Several instruments are usually carried onboard a magnetospheric spacecraft to estimate this key physical parameter. In the case of the ESA/NASA Cluster mission, composed of 4 satellites, four different instruments on each platform can be used to estimate it: two particle instruments (electrons and ions), a DC electric field instrument, a relaxation sounder (an active wave instrument) and a high-time resolution passive wave receiver. Each of these instruments has its own limitations depending on the plasma conditions.
{ } The Earth^'s magnetotail is indeed far from being a uniform medium but instead composed of regions with distinct electron density (Ne) and temperature (Te) ranges, including: the lobe regions (Ne < 0.01 cm^-3, Te ~ 100 eV) and the plasmasheet (0.1 - 1.0 cm^-3, Te ~ 1 keV).
{ } Particle instruments can be blind to low energy ions coming from the ionosphere or measuring only a portion of the energy range of the particles. This results in an under estimation of the total density. Photoelectrons are also perturbing the density measurements and careful analysis of the spacecraft potential is necessary. Measurements from a relaxation sounder also require careful calibration and on Cluster can not be used to estimate densities below 0.2 cm^-3 (lower frequency of the instrument soundings).
{ } Case studies will be presented comparing simultaneous electron density estimation from particle instruments, DC electric field instrument and the relaxation sounder. This latter instrument has been rarely used in the past to derive the total electron density in the distant tail. The outcome of an extensive analysis of the relaxation sounder measurements in the magnetotail by Cluster will be presented. The results will show under which plasma conditions and how the total electron density can be extracted from these measurements, which offer to the particle instruments an independent and complementary estimation of the density.
DE: 2744 Magnetotail
DE: 2794 Instruments and techniques
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Fall Meeting