High Latitude Current Systems: FAST and Polar Observations

Details High Latitude Current Systems: FAST and Polar Observations High Latitude Current Systems: FAST and Polar Observations

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsm42a0591s&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SM42A-0591

Computer Science

Databases

2407 Auroral Ionosphere (2704), 2409 Current Systems (2708), 2704 Auroral Phenomena (2407), 2708 Current Systems (2409), 2736 Magnetosphere/Ionosphere Interactions

Scientific paper

The polar-orbiting FAST and Polar spacecraft have provided extensive observations of the field-aligned current (FAC) systems that flow into and out of the high latitude ionosphere. These FACs flow in response to the forces that act on the magnetospheric and ionospheric plasmas; the classical Region-1, -2 current sheet model is the analog to the twin cell convection pattern associated with steady southward Interplanetary Magnetic Field. The FAST and Polar observations have demonstrated both the strengths and weaknesses of the Region-1, -2 current sheet model. Large statistical databases show that the Region-2 current system is closed within the inner magnetosphere by a partial ring current, while investigations of the large scale current system in the dawn-dusk meridian show that ~70% of the Region-1 currents are coupled to the Region-2 currents, as required to provide the return flow over a narrow latitude range. On the other hand FAST and Polar observations in the dayside cusp region demonstrate some of the problems with the simple Region-1, -2 model. The cusp currents are strongly dependent on IMF orientation, but it is by no means clear what the field-aligned current morphology actually is in this region. Models of cusp currents include overlapping Region-1 currents, separate polar cap DPY currents, and hybrid current sheet models, where one of the cusp currents is part of the Region-1 system, and the other is a polar cap FAC. Understanding the morphology of these currents requires knowledge of the underlying magnetic field topology, including both the transition from open to closed field-lines, and the mapping of open field lines to the magnetopause, as the magnetic field topology relates the FACs to the drivers of convection. Similar problems manifest themselves when considering observations of multiple FAC sheets in the dawn-dusk meridian. Are the additional FACs structures within the Region-2 currents, or structures within the Region-1 currents? Or is trying to place these currents into the Region-1, -2 model misleading, if not simply wrong? Again knowledge of the magnetic field topology is essential in resolving these questions. Several resources are available to address this issue, including in situ particle observations, ground-based ionospheric observations, and MHD models.

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