High‐latitude irregularities of the magnetospheric electric field and their relation to solar wind and geomagnetic conditions

Abstract

Having processed high‐resolution electric field measurements of the low‐altitude spacecraft Dynamic Explorer 2 in order to reveal and study signatures of rapid magnetospheric streams, we found that along with a regular large‐scale electric field there exists an irregular one with amplitudes of 50–200 mV m−1 and transverse scale sizes varying from several to a hundred kilometers. This component behaves quite differently compared to the regular field: In particular, it is most common and of highest intensity under strong northward Bz interplanetary magnetic field (IMF) and low AE and Dst conditions. Thus low average electric field (as expected and observed at quiet times) does not mean low variance. Large‐amplitude electric field fluctuations typically occur at or around the convection reversal boundary, expanding to the central polar region or shifting to the equator depending on Bz IMF direction. They are accompanied by large variations of the magnetic field component, with one‐to‐one correspondence of peaks and valleys of electric and magnetic field oscillations. The field‐aligned currents inferred are on the order of 10–100 A km−2, which is large enough to be associated with discrete arcs.