Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsm24a..03w&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #SM24A-03
Physics
2731 Magnetosphere: Outer, 2740 Magnetospheric Configuration And Dynamics, 2744 Magnetotail, 2760 Plasma Convection (2463), 2764 Plasma Sheet
Scientific paper
The spatial variations of PV5/3 and nV, where P is total plasma pressure, n is number density, and V is the flux tube volume per unit magnetic flux, are crucial to understanding the large-scale plasma transport and its associated energy transfer in the plasma sheet. We have used 10 years of Geotail data and a formula for estimating V to investigate statistically the equatorial distributions of ion PV5/3 and nV in the nightside plasma sheet between r = 10 to 30 RE. We have examined the distributions under three different conditions according to the cross polar-cap potential drop and AE index: (1) weak convection and low geomagnetic activity, (2) enhanced convection and low geomagnetic activity, and (3) enhanced convection and high geomagnetic activity. The overall nV is seen to decrease significantly with increasing convection or activity, but the overall PV5/3 remains similar. The decrease of nV can be seen when convection increases during the same low activity, suggesting that a decrease of source particles, likely the cold particles from the flanks, may play an important role. We compared the variations of PV5/3 and nV along drift paths with the physical bases of ideal MHD and the Rice Convection Model (RCM). We found that PV5/3 drops significantly earthward along the estimated electric drift paths near midnight, indicating that it is far from the assumption d(PV5/3)/dt = 0 used in ideal MHD. Examination of PkV5/3 and the electric and magnetic drift paths of different energy invariants, where Pk is the partial pressure of a specific energy invariant, shows that the strong duskward drift of the above thermal-energy particles due to the magnetic drift, together with there being significantly fewer higher-energy particles from the dawn flank than from the tail, result in the strong earthward decrease of PV5/3. We also found that PkV5/3 does not change significantly along the electric and magnetic drift paths of particles with energies above the thermal-energy, indicating d(PkV5/3)/dt = 0 used in the RCM is a good approximation for the pressure-bearing plasma sheet ions. These comparisons show that the RCM physics can better account for large-scale plasma sheet thermodynamics.
Lui Alberto
Lyons Larry R.
Nagai Takaya
Wang Chenjie
Weygand James M.
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