Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsm33d..04w&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #SM33D-04
Physics
2730 Magnetosphere: Inner, 2753 Numerical Modeling, 2764 Plasma Sheet, 2778 Ring Current, 2788 Magnetic Storms And Substorms (7954)
Scientific paper
The quiet time plasma sheet is an important particle source for the storm-time ring current, and this source depends significantly on interplanetary conditions. To investigate this dependence, we have analyzed 11 years of Geotail data to obtain plasma sheet distributions, and have sorted the northward IMF plasma sheet into 8 different interplanetary conditions based on |IMF Bz| (< 2 or > 2 nT), solar wind density (Nsw, < 6.5 or > 6.5 cm-3), and solar wind speed (Vsw, < 400 or > 400 km/s). We have also used the Magnetospheric Specification Model (MSM) and Tsyganenko 96 magnetic field model to simulate the plasma distributions at r = 6.6 RE resulting from earthward penetration of the observed plasma sheet to obtain an interplanetary condition dependent source distribution for modeling the storm-time ring current. The MSM simulates the electric and magnetic drift of ions. For all conditions, we find that the density is higher near the flanks than near midnight while the temperature is higher in the pre-midnight than the post-midnight sector. We find that the overall density (temperature) is the highest (lowest) during |IMF Bz| > 2, Nsw > 6.5, and Vsw < 400 (condition (1)), while the overall density (temperature) is the lowest (highest) during |IMF Bz| < 2, Nsw < 6.5, and Vsw > 400 (condition (2)). The differences in the densities and temperatures between the two conditions are about a factor of ~ 3. For condition (1) there is abundant low-energy particles (< ~ 3 keV) in the postmidnight sector extending from the dawnside flank to small r (~ 8 RE) near midnight, which is not seen for condition (2), whereas condition (2) has abundant high-energy ions in the pre-midnight sector in the near-Earth plasma sheet. Conditions (1) and (2) represent two extremes of the northward IMF plasma sheet, which we have used as initial conditions for simulating the storm-time plasma sheet under enhanced convection and earthward penetrating electric fields. We found that condition (1) leads to a strong pressure peak in the post-midnight sector in the inner magnetosphere, whereas condition (2) leads to a much smaller pressure peak (by a factor of ~ 2) centered at midnight at larger r. This indicates that the particle sources for the storm-time ring current can be strongly affected by the plasma sheet state before storms, which depends strongly on the pre-storm interplanetary conditions. Chen et al. (this meeting) used our simulation results at r = 6.6 RE as boundary conditions for self-consistent ring- current simulations to investigate how these two plasma sources affect the local time asymmetries in storm- time ring current development.
Lyons Larry R.
McEntire Richard W.
Nagai Takaya
Wang Chenjie
Weygand James M.
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