Earthward electric field in the magnetotail: Cluster observations and theoretical estimates

Abstract

In this paper we present an experimental evidence of the existence of the earthward electric field in the thin current sheet of the Earth magnetotail. This field plays an essential role in the redistribution of observed intensities of cross‐tail proton and electron currents. We consider the statistics of 59 thin current sheet crossings observed by CLUSTER spacecraft. It is shown that the sum of electron diamagnetic and curvature drifts can explain less than a half of the value of electron bulk velocity. The remaining part of electron velocity is thus related to the Ex × Bz cross field drift. The measurements of the typically negative shift of the central part of proton velocity distribution also confirm the existence of positive Ex field. Finally we suggest the mechanism of Ex formation in the thin current sheet of the Earth magnetotail.