HR: 0830h
AN: SM21B-0198    [PDF]
TI: Bifurcated current sheet : Model, CLUSTER observations and analysis of MHD wave propagation
AU: * Genot, V
EM: vincent.genot@cesr.fr
AF: CESR/CNRS, 9 Av. Colonel Roche, Toulouse, 31400 France
AU: Fruit, G
EM: gabriel.fruit@cesr.fr
AF: CESR/CNRS, 9 Av. Colonel Roche, Toulouse, 31400 France
AU: Louarn, P
EM: philippe.louarn@cesr.fr
AF: CESR/CNRS, 9 Av. Colonel Roche, Toulouse, 31400 France
AU: Mottez, F
EM: fabrice.mottez@cetp.ipsl.fr
AF: CETP/CNRS, 10-12 Av. de l'Europe, Velizy, 78140 France
AU: Sauvaud, J
EM: sauvaud@cesr.fr
AF: CESR/CNRS, 9 Av. Colonel Roche, Toulouse, 31400 France
AU: Balogh, A
EM: a.balogh@ic.ac.uk
AF: Space and Atmospheric Physics, Imperial College, London, SW7 2BZ United Kingdom
AB: CLUSTER observations have recently confirmed previous GEOTAIL observations showing that the magnetotail current sheet can present a bifurcated structure with two off-centre current peaks. Such structures may be described by a kinetic tangential equilibrium which is an exact solution of the Vlasov-Maxwell equations. A tangential equilibrium is characterized by a bulk plasma velocity and magnetic field perpendicular to the density and/or temperature gradient direction. The particle distribution functions are described by an infinite sum of elementary functions parametrized by a vector potential. The model is consistent with CLUSTER observations of a plasma density plateau between the current peaks and the typical size and amplitude of the current distribution. Fitting field and density measurements of the bifurcated current sheets enables us to characterize the required model particle distribution functions, which are then compared with CLUSTER data. Using this semi-analytical model, we analyze the propagation of compressive MHD perturbations in a bifurcated plasmasheet by explicitly solving the linear response of the sheet to an impulsive perturbation, as performed in a companion paper [Fruit et al.]. Due to the relative homogeneity of the plasma in the centre of the bifurcated sheet, very low frequency mode waves are not as quickly damped as in a Harris-like sheet. We exhibit this behaviour by evaluating the temporal and spatial variations of the wave absorption rate in the sheet. These results are finally compared to CLUSTER data and lead to the suggestion that observations of very low frequency modes may be interpreted as MHD perturbations.
DE: 2409 Current systems (2708)
DE: 2744 Magnetotail
DE: 2753 Numerical modeling
DE: 7827 Kinetic and MHD theory
SC: SPA - Magnetospheric Physics [SM]
MN: 2003 Fall Meeting