Distribution of hydrogen and oxygen ion species in the plasmasheet

Abstract

In this paper, using data obtained by Cluster 4 satellite from 2001 to 2012, we statistically investigate the spatial distributions of H+ and O+ in the magnetotail plasmasheet and their relation with geomagnetic indices. Our work outlines the existence of two regions with enhanced O+ concentration in the tail plasmasheet, one is located in the mid-tail plasmasheet at R>17RE, and the other is located near the inner boundary of plasmasheet at R<10RE. The existence of the depletion region of O+ between 10RE<R<17RE indicates that the O+ ions in the mid-tail plasmasheet, which come from polar cap, are not likely to be able to make important contribution to the formation of ring current. Both the distributions of density and temperature of O+ ions have a dawn–dusk asymmetry. The number density of O+ during geomagnetic active time (Dst<−20nT/AE>200nT/Kp⩾3) is much larger than that during non-storm time (Dst>−20nT/AE<200nT/Kp<3). This dawn–dusk asymmetry and the number density of O+ varying with geomagnetic activity apply for both regions (R<10RE and R>17RE) of O+. Therefore both substorm and enhanced convection provide a large number of O+ ions to the plasmasheet, which makes favorable condition for the growth of the ring current.