Modes of high‐latitude electric field variability derived from DE‐2 measurements: Empirical Orthogonal Function (EOF) analysis

In this study we characterize dominant modes of 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, 11 EOFs are capable of representing 68% of the squared electric field in the original data, leaving only a fairly random component as a residual. While such mathematically independent EOFs do not necessarily represent physically independent modes of variability, each of the first two EOFs is actually related to a widely known physically prominent effect on the convection patterns. Variability associated with the interplanetary magnetic field (IMF) BY component emerges as the primary mode, and variability associated with the IMF BZ effect emerges as the secondary mode. The tertiary mode reflects variability in the cusp region, but is not significantly correlated with the IMF.