Electric field measurements in the inner magnetosphere by Cluster EDI

Abstract

We report electric field measurements in the inner magnetosphere from the Electron Drift Instrument (EDI) on Cluster at distances of 4 < L < 10. The data used in this study span more than 1 year so that all local times are covered. Both components of the electric field perpendicular to the ambient magnetic field are mapped into the equatorial plane with the magnetic field model of Tsyganenko and Stern [1996]. Average values and standard deviations are sorted by the polarity of the BZ component of the interplanetary magnetic field (IMF). Average Kp values for both BZ polarities are 1.45 (BZ > 0) and 2.45 (BZ < 0). These electric fields are discussed in terms of their sources such as the ionospheric dynamo and the solar wind‐magnetosphere interaction. We also quantify the electric field as follows: the average shielding parameter γ [Volland, 1973; Stern, 1975] is ∼2, although the value for southward IMF is smaller than the value for northward IMF. The parameter γ is larger on the duskside than in the dawn sector. The average rate of sunward transport of magnetic flux, equivalent to the duskward electric field, is estimated as 0.32 mV/m for southward IMF. Finally, fluctuations tend to be larger than the DC component around the stagnation point, which could lead to outflow of plasmaspheric material.