Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)




Jan J. Sojka


The high-latitude electric eld fall-o region connects convection in the polar cap to the region where ring currents modify the penetration electric field equatorward of the polar cap boundary. This region is often overlooked because it falls between the limits of low latitude and high-latitude ionospheric models. However, penetrating electric fields cause large changes in ion composition; and therefore, correctly modeling the electric fields and plasma drift in this region aids in correctly specifying the ionosphere. Many ionospheric models use the Kp index as a physical driver, and so the latitude dependence of the plasma drift in the fall-o region was investigated as a function of Kp using Defense Meteorological Satellite Program ion drift data from the 2007{2010 solar minimum. Both the dusk and dawn sectors were analyzed and t to analytical functions describing the fall-o with decreasing latitude. The latitude dependencies were found to dier in the dusk and dawn sectors with a factor of two increase in the expansion of the duskside polar cap radius and auroral region over the dawnside. Additionally, the low-Kp polar cap radius was found to be five degrees smaller than the radius currently used in simple ionospheric models.



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