Physics
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsm52a0566e&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #SM52A-0566
Physics
2720 Energetic Particles, Trapped, 2730 Magnetosphere: Inner, 2736 Magnetosphere/Ionosphere Interactions, 2753 Numerical Modeling, 2778 Ring Current
Scientific paper
A comprehensive ring current simulation has been performed in a self-consistent manner to understand the post-midnight enhancement of tens of keV ion fluxes during the storm main phases. The post-midnight enhancements of the ion fluxes, which are different from a traditional picture, were recently discovered by the IMAGE satellite through energetic neutral atom images, but their mechanism is still debatable. Three possible working hypotheses were suggested and carefully tested. First, skew of the convection electric field is thought to shift the peak of the flux. Second, a decrease in the local magnetic field induced by the ring current itself deflects drift trajectories eastward. Third, local time asymmetry of the distribution function of the near-earth plasma sheet is also a candidate. Two feedback loops were implemented in the calculation to update electric and magnetic fields at each time step. The first loop, electric coupling between the magnetosphere and the ionosphere, is completed by combining Fok's ring current model and the Rice Convection Model. The second loop is newly introduced by constantly updating the magnetic field induced by the calculated ring current. The result shows that the spatial distribution of ion fluxes is significantly modulated by these feedback loops. The post-midnight enhancement is shown to be predominantly produced by the skew of the convection potential modulated by the gradient of the ionospheric conductivity, and shown to depend on the distribution function of plasma sheet ions. The self-consistent magnetic field seems not important for generating the post-midnight enhancement, but is shown to produce a localized enhancement of ion fluxes in L on the dusk side with energy of tens of keV and less. This feature is consistent with measurements made by Polar during the storm main phases.
C:son Brandt Pontus
Ebihara Yasuhiro
Fok M.-
Moore Thomas Earle
Wolf Richard A.
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