Modes of the High-Latitude Electric Field Variability Derived From DE-2 Measurements: Empirical Orthogonal Function (EOF) Analysis

In this study we characterize dominant modes of the high-latitude electric field variability as a set of two-dimensional empirical orthogonal functions (EOFs), based on a sequential non-linear regression analysis of the electric field derived from plasma drift measurements during the Dynamics Explorer-2 (DE-2) satellite mission (1981-1983). Together with the mean fields, the 11 EOFs are capable of capturing 68% of the total electric field variability, leaving only a fairly random component as a residue. While such mathematically independent EOFs do not necessarily represent physically independent modes of variability, each of the first two EOF is actually related to a widely known physically prominent effect on the convection patterns. In brief the variability associated with the interplanetary magnetic field (IMF) By component emerges as the primary mode, and the IMF Bz effect emerges as the secondary mode. The tertiary mode seems to reflect the variability in the cusp region, which may also be associated with the IMF By effect.