HR: 1340h
AN: SM13B-1324    [Abstracts]
TI: The Relationship Between Convection Velocities in Simultaneous High-Latitude Ionospheres
AU: * Shepherd, S G
EM: simon.g.shepherd@dartmouth.edu
AF: Thayer School of Engineering, Dartmouth College, 8000 Cummings Hall, Hanover, NH 03755, United States
AU: Murr, D L
EM: David.Murr@Dartmouth.edu
AF: Thayer School of Engineering, Dartmouth College, 8000 Cummings Hall, Hanover, NH 03755, United States
AU: Ruohoniemi, J M
EM: Mike.Ruohoniemi@jhuapl.edu
AF: The Johns Hopkins University Applied Physics Laboratory, Johns Hopkins Road, Laurel, MD 20723, United States
AB: Depending on the dipole tilt angle of the Earth's magnetosphere, the northern and southern hemispheres can have dramatically different average conductances. Because the ionosphere provides a path through which magnetospheric field-aligned currents coupling the two regions close, it is expected that the electric field and current density would also exhibit asymmetric behavior between hemispheres that depend on the dipole tilt angle. Some magnetohydrodynamic models of the magnetosphere show that the ratio of the global hemispheric electric potential can be a factor of 2-4 for large dipole tilt angles. Statistical studies of ionospheric electric fields using ground-based radars and spacecraft also show that there is a seasonal dependence of the global ionospheric potential but that the difference is at most ~20%. Here we use merged line-of-sight velocity vectors obtained simultaneously in both hemispheres from the SuperDARN network of HF radars to investigate the relationship of the convection velocity for conditions of varying hemispheric conductance. We find a marked difference in the hemispheric relationship of the simultaneous convection velocities between the dayside and the nightside ionospheres. Using a dataset consisting of seven years of SuperDARN merged velocities centered roughly on the most recent solar maximum, we show statistically that the ratio of velocities restricted to the dayside in the Summer hemisphere to those in the dayside Winter hemisphere depends only marginally on the dipole tilt angle and is at most a factor of ~1.2 for extreme tilt angles. The ratio of merged velocities restricted to the nightside, however, show a strong dependence on dipole tilt angle and can be as high as 2 for extreme tilt angles. The results are consistent with the notion that the dayside magnetosphere-ionosphere circuit behaves as if driven by a constant voltage source, whereas the nightside acts more like a circuit with a constant current source.
DE: 2736 Magnetosphere/ionosphere interactions (2431)
DE: 2740 Magnetospheric configuration and dynamics
DE: 2760 Plasma convection (2463)
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Fall Meeting