Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm14b..07w&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SM14B-07
Physics
[2724] Magnetospheric Physics / Magnetopause And Boundary Layers, [2728] Magnetospheric Physics / Magnetosheath, [2764] Magnetospheric Physics / Plasma Sheet
Scientific paper
An entry process that transports and energizes ions and electrons differently as these particles move from the magnetosheath into the plasma sheet can result in a change in the ion to electron temperature ratio. In this study we have investigated 3 years of THEMIS data to determine the ratio in the nightside plasma sheet beyond X = -10 Re and how it correlates with the ratio in the magnetosheath. The ratio in the magnetosheath is found to strongly depend on the upstream solar wind speed, with median ratio increasing from around 5 to 10 as the solar wind speed increases from 350 to 650 km/s. The ratio in the magnetosheath shows no clear dawn-dusky asymmetry and no dependence on the downtail distance. For the plasma sheet data, we fitted each particle energy spectrum with a two-component (one hot and one cold) kappa distribution and defined the plasma sheet being hot (cold) if the number density for the hot (cold) component is larger than that of the other component. The ion to electron temperature ratio in the plasma sheet decreases as plasma becomes hotter. When the plasma sheet is hot, the median ratio (around 3) is substantially lower than that in the magnetosheath and it does not change significantly with either the location or solar wind speed. However, when the plasma sheet is cold, the ratio is low near midnight (smaller than 4) but increases with increasing |Y| with the ratios near the two flanks (around 10 at the dusk flank and 7 at the dawn flank) being very close to the ratio in the magnetosheath. However, along the two flanks, only the ratio near the dusk flank is found to have the same dependence on the solar wind speed as that seen in the magnetosheath. This suggests that the dominant entry processes at the two flanks may be different if the cold plasma sheet plasma near the flanks are particles newly entering from the magnetosheath. The above results provide observational constraints for the temperature ratios predicted by different competing entry mechanisms.
Angelopoulos Vassilis
Lyons Larry R.
Wang Chenjie
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