Substorm Onset by Plasma Sheet Divergence

Details Substorm Onset by Plasma Sheet Divergence Substorm Onset by Plasma Sheet Divergence

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsm22d..01l&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SM22D-01

Physics

2431 Ionosphere/Magnetosphere Interactions (2736), 2736 Magnetosphere/Ionosphere Interactions, 2764 Plasma Sheet, 2788 Storms And Substorms

Scientific paper

It is necessary to understand current wedge formation in order to understand the cause of the substorm expansion phase. Geotail spacecraft observations have shown that the inner-plasma-sheet cross-tail current reduction within the current wedge results from a process that leads to a reduction in equatorial plasma pressure and a substantial reduction in flux tube ion content. We use the single-species continuity equation for plasma sheet particles to identify a plausible cause of these plasma reductions. We find that a convection reduction, which follows a growth phase period of enhanced convection, should cause a divergence of plasma sheet particles driven by diamagnetic drift that leads to flux tube content reduction. Such reduction in flux tube content is longitudinally localized to the pre-midnight to midnight region where the current wedge has been observed to initially form and must initiate within the region of the equatorial mapping of the Harang discontinuity, consistent with ionospheric observations of substorm onset. We also find that the reduction in flux tube content should initially develop slowly, and then develop more rapidly as the current wedge forms. This is consistent with observations which show that expansion phase aurora, and thus also the current wedge, develops slowly for a few minutes before brightening rapidly, and it is as required if plasma sheet divergence driven by diamagnetic drift leads to current wedge formation and initiation of the substorm expansion phase.

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