Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm33b1901w&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM33B-1901
Physics
[2706] Magnetospheric Physics / Cusp, [2723] Magnetospheric Physics / Magnetic Reconnection, [2724] Magnetospheric Physics / Magnetopause And Boundary Layers, [2764] Magnetospheric Physics / Plasma Sheet
Scientific paper
Cold dense plasma sheet (CDPS) material is found along the flanks of the magnetopause during extended intervals of northward interplanetary magnetic field (IMF). The source for this population is the magnetosheath, and an un-resolved question is what mechanisms dominate in transporting, heating and accelerating it. Northward IMF is thought to be favorable for the Kelvin-Helmholtz instability (KHI), which can lead to turbulent mixing of plasma across the magnetopause. It is also thought favorable for high-latitude reconnection behind the cusps, which can permit direct injection and acceleration of particles. When newly-reconnected, cusp field lines on the day side contract due to magnetic tension, producing a characteristic velocity dispersion with faster particles arriving near Earth while field lines are still at higher latitudes (dE/dILAT~> 0). The low-altitude FAST spacecraft often observed overlapping energy dispersed ions (EDIs) during periods of northward IMF, leading to speculation that these signatures may be a near-Earth manifestation of CDPS material. These EDIs are a major focus of the present study. Our survey of FAST observations shows that during extended northward IMF intervals more than 80% of EDIs have dE/dILAT~> 0. A similar fraction of events have loss cones consistent with mirroring in the near hemisphere, suggesting that strong pitch-angle scattering is common and able to erase prior mirroring signatures. In contrast, during extended intervals of southward IMF EDIs shift location from the flanks to the night side, which might be expected for injection in the tail. For these, a little less than half show dE/dILAT~< 0, as would be expected for velocity dispersion during dipolarization. This suggests that adiabatic energization during field line relaxation can overcome velocity filtering effects. We also have examined a large number of CDPS events observed by Cluster and often find energy dispersed ions. These have loss cones that also correspond to mirroring in the near hemisphere, but we cannot establish that these have a high latitude injection source. Although conjugate observations are rare, we have found some simultaneous FAST data, which show dispersion with dE/dILAT~> 0, lending some support to a lobe reconnection source.
Brown Katrina
Hull Arthur J.
McFadden James P.
Teste A. F.
Wilber M. M.
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