Typical values of the electric drift <b>E</b> \texttimes <b>B</b> / <i>B</i> <sup>2</sup> in the inner radiation belt and slot region as determined from Van Allen Probe measurements

The electric drift E \texttimes B/B2 plays a fundamental role for the description of plasma flow and particle acceleration. Yet it is not well-known in the inner belt and slot region because of a lack of reliable in situ measurements. In this article, we present an analysis of the electric drifts measured below L ~ 3 by both Van Allen Probes A and B from September 2012 to December 2014. The objective is to determine the typical components of the equatorial electric drift in both radial and azimuthal directions. The dependences of the components on radial distance, magnetic local time, and geographic longitude are examined. The results from Van Allen Probe A agree with Van Allen Probe B. They show, among other things, a typical corotation lag of the order of 5 to 10\% below L ~ 2.6, as well as a slight radial transport of the order of 20 m s-1. The magnetic local time dependence of the electric drift is consistent with that of the ionosphere wind dynamo below L ~ 2 and with that of a solar wind-driven convection electric field above L ~ 2. A secondary longitudinal dependence of the electric field is also found. Therefore, this work also demonstrates that the instruments on board Van Allen Probes are able to perform accurate measurements of the electric drift below L ~ 3.
Year of Publication
Journal of Geophysical Research: Space Physics
Date Published