Electrodynamic patterns for September 19, 1984

Abstract

Variations of the northern high‐latitude ionospheric convection pattern are estimated from combined ground‐based and satellite‐based measurements for the disturbed day of September 19, 1984, during the Equinox Transition Study (ETS) campaign period. The electric potential distribution is determined from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure of Richmond and Kamide (1988) on the basis of available electric field, conductance, and magnetic perturbation observations. As an improvement over previous data inversion studies of high‐latitude electrodynamics, we have incorporated satellite measurements of precipitating particles to help determine variations of the conductances in the auroral oval. These measurements are found to cause substantial modifications to the initial empirical conductance model. A large substorm commenced about 0920 UT and peaked about 1050 UT, followed by smaller substorms starting about 1430 UT and 1800 UT. The polar‐cap potential drop varied between about 30 kV and 160 kV during the day, and the integrated Joule heating over the northern polar region varied between 3×109 W and 8.6×1011 W. During the substorms the derived convection potential was considerably enhanced and distorted with respect to the empirical model of Foster et al. (1986). Strong eastward convection in the midnight sector of the auroral oval during the first large substorm was associated with a marked westward rotation of the two‐cell convection pattern at the peak of the substorm. These variations can be expected to have influenced significantly the dynamics of the high‐latitude ionosphere and thermosphere during the ETS period.