Relation between the ring current pressure and mid-latitude electric fields

P. C. Brandt, J. Goldstein and J. C. Foster


It has been known that a strong poleward electric field is created in the 
evening sector at sub-auroral latitudes during mainphases of geomagnetic 
storms (e.g. Southwood and Wolf, 1978; Galperin, 1974).  Recently, ground
observation efforts from Millstone Hill Radar, GPS receiver stations have 
related these phenomena to high sunward flow velocities and enhanced 
electron densities in a narrow latitudinal band at sub-auroral latitudes, 
Sub-Auroral Polarization Streams (SAPS) and directly related them to the 
so-called plasmaspheric drainage plume (Foster et al., 2002). The working 
hypothesis is as follows: (1) The ring current pressure increases around 
midnight during the mainphase. (2) The Region 2 current (R2C) intensifies 
due to increase pressure gradients in the ring current. (3) Large 
conductivity gradients in the ionosphere together with the intensified 
currents and enhanced convection are responsible for setting up the SAPS. 
Goldstein et al. (this meeting) have shown the effect of the SAPS on the
plasmasphere and found that it strips of the outer layers of the evening 
plasmapause pointing at the effects of the SAPS formation. To illuminate 
the causes/drivers for the SAPS, we will investigate the relation between 
the build-up of the ring current and the enhanced ionospheric densities in 
the region of the SAPS.  We use total electron content (TEC) derived from 
GPS receivers and satellites.

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Presented at the August 2003 AGU Chapman Conference, Helsinki, Finland