Physics
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsm11b..06w&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SM11B-06
Physics
2463 Plasma Convection (2760), 2731 Magnetosphere: Outer, 2744 Magnetotail, 2753 Numerical Modeling, 2764 Plasma Sheet
Scientific paper
Cold particles (<1 keV) from the flanks are an important source for the plasma sheet population. However, the transport of these particles within the plasma sheet and how they affect the entropy of the plasma sheet is not well understood quantitatively. We have analyzed 11 years of Geotail data to estimate drift velocities and diffusion coefficients as a function of plasma sheet locations and the direction of the IMF Bz. The drift directions are in general toward the Earth and toward the flanks, and the drift speed is stronger during southward IMF. The diffusion coefficients are found to be higher with increasing distance from the Earth, higher near midnight than near the flanks, and higher during southward IMF. We have used the estimated drift velocities and diffusion coefficients to simulate the spatial distributions of phase space densities at different energies resulting from drift and diffusion of particles from flank sources. The comparisons between the simulation results and the Geotail distributions indicate that diffusion is important to the transport of cold particles and that the flank particle sources are stronger during northward IMF. The simulations show that strong diffusion, which is directed mainly toward midnight, allows the cold particles from the flanks to overcome electric drift, which is directed mainly away from midnight, to have access to midnight. The number of particles resulting from the combined transport decreases with increasing distance from the flanks. Since they are cold, the inward transport of the particles from the flanks leads to a significant increase in the plasma sheet density, but its contribution to pressure is small. Thus the flank particles are not likely to significantly enhance entropy of the plasma sheet or lead to a tail pressure crisis.
Lyons Larry R.
Nagai Takaya
Wang Chenjie
Weygand James M.
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