Paper#: 39
Poster #:
Session Name: Workshop 1C: High Latitude Processes
Room: West Ballroom
Day: Monday
Time: 3:45-4:10 p.m.
Abstract Title: Electrodynamics of the Nightside Auroral Bulge from Freja and Astrid-2 Observations
PresentSurname: Marklund, G.
All Authors: G. Marklund, T. Karlsson
Abstract : Results on the electrodynamics of the nightside auroral bulge with particular emphasis on field-aligned current closure are presented based on simultaneous satellite and ground-based observations and numerical simulation studies. Two events are discussed, one during typical substorm conditions when the Freja satellite crossed the surge head close in time to substorm onset, and the other during steady magnetospheric convection conditions, when the Astrid-2 satellite moved across a conductivity gap between the eveningside and morningside convection cells. For both events, the large-scale field-aligned currents (FAC) associated with the bulge are shown to be closed locally rather than remotely and the current closure could not be described according to the Cowling current model. Results from numerical simulations of FACs associated with the auroral surge are presented for various combinations of remote and local current closure which support the findings from the event studies. These results imply a tail current disruption characterized by filamentary and balanced FACs rather than a distributed large-scale FAC system, at least for the earlier parts of the substorm and auroral bulge development.