High‐latitude ionospheric electric field variability and electric potential derived from DE‐2 plasma drift measurements: Dependence on IMF and dipole tilt

Abstract

In this study the characteristics of electric field variability are investigated by using the sample standard deviations estimated from plasma drift measurements obtained during the Dynamics Explorer 2 (DE‐2) mission. The spatial distribution of the standard deviation over the area poleward of 45° magnetic latitude and its climatological behavior with respect to the magnitude and orientation of the interplanetary magnetic field (IMF) and the dipole tilt angle (season) are examined. In comparison with past studies based on ground‐based measurements and with results from a data assimilation model, this study quantifies the electric field variability with more complete spatial coverage and with more extensive climatological information and therefore is of importance to the problem of the global Joule heating estimation in thermospheric general circulation modeling. In general, the magnitude of the standard deviation exceeds the strength of the mean electric field in most of the polar area, especially under northward IMF conditions. In contrast to the climatological electric field, whose magnitude tends to be most intense in the polar cap, the standard deviation generally intensifies in the vicinity of the convection reversal and the cusp. Under most IMF clock angles the area of the largest electric field variability lies near the cusp; under the southward BZ condition the area extends toward the potential maximum on the dawn side and toward the region of strong sunward convection in the afternoon, while under the positive BY condition the area extends poleward of the potential maximum on the dawn side. The analysis reveals that electric field variability varies with magnetic latitude, magnetic local time, IMF, and season in a manner distinct from that of the climatological electric field. This indicates that empirical models and data assimilation models designed to reproduce the average electric potential or the average electric fields correctly are not necessarily well‐suited to represent the squared electric fields or the electric field variability correctly.