Local time resolved dynamics of field‐aligned currents and their response to solar wind variability

Abstract

AbstractUsing 10 years of CHAMP measurements condensed into the empirical model of field‐aligned currents through empirical orthogonal function analysis, the dynamics of field‐aligned currents (FACs) is modeled and studied in separate magnetic local time (MLT) sectors. We investigate the distributions of FAC intensity and latitude and evaluate their predictability in terms of geospace parameters which are ranked according to their relative importance measured by a multivariate regression procedure. The response time to changes in solar wind variables is studied in detail and found to be much shorter for dayside FACs than on the nightside (15–25 min versus 35–95 min). Furthermore, dayside FACs can be parameterized more accurately: R2 values maximize greater than 0.7 for FAC latitude and greater than 0.3 for FAC intensity, whereas the corresponding values on the nightside are smaller than 0.3 and 0.15, respectively. The results support the separation between directly driven coupling processes acting on the dayside and unloading processes controlling the nightside. In addition, the MLT‐resolved standardized regression coefficients suggest that (1) FAC latitude is affected most significantly by the transpolar potential, substorm evolution, solar activity as represented by the F10.7 index and its square, and the dipole tilt; (2) Region‐1/2 current intensity is controlled most efficiently by substorm evolution, IMF Bz and IMF By; and (3) cusp current intensity is influenced by conductivity, IMF By and their cross item.