Cluster observations of energy conversion regions in the plasma sheet

Abstract

Cluster allows for the first time a systematic examination of energy conversion, by the evaluation of the power density, E · J, with E the electric field and J the current density. Following a careful inspection of the Cluster plasma sheet data from the summer and fall of 2001, we selected 43 energy conversion regions (ECRs), out of which 26 concentrated load regions (CLRs, E · J > 0) and 17 concentrated generator regions (CGRs, E · J < 0). As expected in the tail, at about 19 RE geocentric distance, the energy conversion is more intense for CLRs, on average some 25 pW=m3, compared to some 5 pW=m3 for CGRs. The CLRs are located closer to the neutral sheet and dominated by E and J in the GSE y direction, unlike the CGRs, that prefer locations towards the plasma sheet boundary layer, where the deviations of E and J from the GSE y direction can be significant. The ECRs are often associated with high speed bulk flows, on average faster and hotter for CLRs. The CLRs appear to be associated also with density drop and sometimes with temperature anisotropy, T|| > T⊥, features which are observed less frequently for CGRs.