Other
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsm22b..11t&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #SM22B-11
Other
2740 Magnetospheric Configuration And Dynamics, 2744 Magnetotail, 2753 Numerical Modeling, 2764 Plasma Sheet, 2784 Solar Wind/Magnetosphere Interactions
Scientific paper
Simple analytical models have been derived for the first time, describing the 2-D distribution (along and across the Earth's magnetotail) of the central plasma sheet (CPS) ion temperature, density, and pressure, as functions of the incoming solar wind and IMF parameters, in the range of distances between 10 and 50 RE. Another result of this effort is a new quantitative model, representing as a~function of the dipole tilt angle the shape of the cross-tail current sheet and its response to varying solar wind and IMF conditions. The models are based on a~large set of data of the Low-Energy Particle (LEP) and Magnetic Field (MGF) instruments, taken by Geotail spacecraft in 1994-1998 and used in the form of 1-min average values of the CPS parameters and magnetic field components. The concurrent solar wind and IMF data were provided by Wind and IMP~8 spacecraft. The overall quality of the modeling was characterized by the correlation coefficient (c.c.) R between the observed and predicted values of a parameter. The CPS ion density N, controlled mostly by the solar wind proton density and by the northward IMF component, is the most unstable characteristic of the CPS, yielding the lowest c.c., RN=0.57. The CPS temperature T, controlled mainly by the solar wind speed V and the IMF Bz, yielded a higher c.c., RT=0.71. The CPS ion pressure P was found to be most effectively controlled by the solar wind ram pressure Psw and by an IMF-related parameter composed of the perpendicular IMF component Bperpendicular to and the sine of half clock angle θ /2. In a striking contrast with N and T, the model pressure P revealed a~very high c.c. with the data, RP=0.95, manifesting approximate force balance in the CPS due to its confinement by the external tail lobe magnetic field. The modeling revealed very little dawn-dusk asymmetry of the CPS beyond 10 RE, consistent with the observed symmetry of the tail lobe magnetic field. The plasma ion density N is the lowest at midnight and grows towards the tail's flanks. Larger/smaller solar wind ion densities and northward/southward IMF Bz result in larger/smaller N in the CPS. In contrast to the density N, the temperature T peaks at the midnight meridian and falls off towards the CPS flanks (so that the dawn-dusk variation of their product, the CPS pressure, is much smaller). Faster/slower solar wind and southward/northward IMF Bz result in a~hotter/cooler CPS. The CPS ion pressure P is nearly constant across the midtail (20-50RE); at closer distances the isobars gradually bend and approximately follow the contours of constant geomagnetic field in the equatorial plane. For northward IMF conditions combined with a~slow solar wind, this transition occurs at much larger distances, reflecting a weaker tail current and hence more dipole-like magnetic field. Geodipole tilt and solar wind effects on the shape of the cross-tail current sheet have been modeled in the range of distances 10-50 RE, using the magnetic field data from the entire near-tail phase of the Geotail operation.
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