HR: 1300h
AN: SM52A-0559    [PDF]
TI: Two different approaches for the inner magnetosphere currents estimation: ion pressure measurements and the curlometer technique, using CLUSTER CIS and FGM data.
AU: * Vallat, C
EM: vallat@cesr.fr
AF: CESR/CNRS, 9 avenue du colonel Roche BP 4346 cedex 4, Toulouse, 31028 France
AU: Dandouras, J
EM: dandouras@cesr.fr
AF: CESR/CNRS, 9 avenue du colonel Roche BP 4346 cedex 4, Toulouse, 31028 France
AU: Parks, G
EM: parks@ssl.berkeley.edu
AF: SSL/university of California, #7450, Centennial Drive, Berkeley, CA 94720-7450 United States
AU: Wilber, M
EM: wilber@ssl.berkeley.edu
AF: SSL/university of California, #7450, Centennial Drive, Berkeley, CA 94720-7450 United States
AU: Dunlop, M
EM: m.dunlop@rl.ac.uk
AF: Rutherford Appleton Laboratory, Space Sciences Division, SSTD, Rutherford Appleton Laboratory Chilton,Oxfordshire, Didcot, OX11 0QX United Kingdom
AU: Kistler, L
EM: kistler@atlas.sr.unh.edu
AF: Space Science Center, University of New Hampshire, 39 College Road, Durham, NH 03824-3525 United States
AU: Reme, H
EM: reme@cesr.fr
AF: CESR/CNRS, 9 avenue du colonel Roche BP 4346 cedex 4, Toulouse, 31028 France
AU: Balogh, a
EM: a.balogh@imperial.ac.uk
AF: Blackett Laboratory, Imperial College, South Kensington campus, London, SW7 2AZ United Kingdom
AB: The inner magnetosphere's electric currents configuration and mapping is one of the keys for understanding current loop closure inside the whole magnetosphere. Development of the ring current as a function of geomagnetic activity is still one of the most interesting aspects about this region. Analyzing thus data from the four CLUSTER spacecraft while passing in the inner magnetosphere (perigee situated at about 4 RE, inclination 90$^\circ$ ), we have been using two different methods to quantify currents in this region. First, based on Maxwell's laws application, the curlometer technique is applied. It is based on four point measurements of the magnetic field, as measured by the four Fluxgate magnetometer instruments onboard Cluster. This allows to determine the current density vector crossing the tetrahedron formed by the spacecraft. Second, based on the general MHD momentum equation, and under simplifying assumptions (static conditions, isotropic distribution,...), we experimentally deduced the perpendicular component of the current density by calculating the pressure gradient between spacecraft. This was done by using the Cluster Ion Spectrometer experiment, which provides full three-dimensional ion distributions (from about 5eV/q to 40 keV/q) with one spacecraft spin time resolution (4 sec) and with mass-per-charge composition determination. Both methods reveal very clear and interesting structures of the current. `Filamentations' of the current are observed in the plasma sheet within the field-aligned currents system, and they appear to be extremely well correlated with low energy protons up-flowing from the ionosphere. Smooth and isotropic structures inside the ring current during low geomagnetic activity are also shown, with a large latitudinal extent. Nevertheless, some unexpected signatures are also observed, such as the inversion of the XGSM current density component during perigee passes, even if not fully understood yet. The comparative study of both methods should allow for the first time to better quantify the offsets induced on the current estimation, and to get a more precise image of the current systems in the inner magnetosphere.
DE: 7807 Charged particle motion and acceleration
SC: SPA - Magnetospheric Physics [SM]
MN: 2003 Fall Meeting