ELECTRIC-POTENTIAL PATTERNS IN THE NORTHERN AND SOUTHERN POLAR-REGIONS PARAMETERIZED BY THE INTERPLANETARY MAGNETIC-FIELD

Electric potential patterns have been obtained from the IZMIRAN electrodynamic model (IZMEM) for the northern and southern polar regions during summer, winter, and equinox. The model is derived from a large quantity of high-latitude ground-based geomagnetic data (above +/- 57-degrees corrected geomagnetic latitude) at all magnetic local time hours. A linear regression analysis technique has been used to obtain the quantitative response of each magnetic observatory to changes of interplanetary magnetic field (IMF) components. Since no ionospheric conductivity model exists specifically for the southern polar region, the statistical model of Wallis and Budzinski (1981) has been applied in both hemispheres. A cross-polar ''background'' potential of approximately 35 kV, derived by Reiff et al. (1981), is used to calibrate IZMEM's potential patterns. The model's responses to changes in the IMF B(y) and B(z) components are analyzed to obtain a set of ''elementary'' convection patterns in both polar regions for each season of the year. Asymmetry in the potential pattern geometry in both hemispheres can be attributed either to the influence of the ''northern'' ionospheric conductivity model which was applied to the southern polar region, or to some natural phenomena. The modeled background cross-polar potential for the condition when B(z) = B(y) = 0 is found to be approximately 37 kV. Average values of the modeled potential drop caused by each nanotesla of the IMF are the following: approximately 14 kV for southward B(z); approximately -4 kV for northward B(z); and approximately +/- 4.5 kV for B(y) components. The latter is not applicable to the ''dawn-dusk'' potential drop; it may be applied across the cusp region only. Nevertheless, a combination of the background and elementary potential patterns in the case studies gives a certain estimation of the cross-polar potential drop, which may be strongly distorted during time of large B(y). It is concluded that IZMEM provides realistic convection patterns parameterized by the IMF component directions and magnitudes and may be used to provide routine estimates of convection patterns and electric potentials if IMF data are available.