Synthesis models of dayside field‐aligned currents for strong interplanetary magnetic field By

Abstract

Using particle and magnetic field data acquired with DMSP‐F6 and DMSP‐F7 satellites, we have investigated interplanetary magnetic field (IMF) By dependence of the global pattern of plasma regime and field‐aligned currents (FACs) on dayside high latitudes during strong IMF By (averaged |By| > 3.7 nT) and geomagnetically disturbed (mainly IMF Bz < 0) periods. From particle data we have identified five plasma regimes: inner plasma sheet, outer plasma sheet, cleft, cusp, and mantle. All the plasma domains except the inner plasma sheet show By dependence in spatial distribution. Region 1 and “traditional cusp” currents appear in cusp/mantle domains, which we call midday region 1 and region 0 currents, respectively, in this paper. These currents perfectly reverse their flow directions depending on IMF By polarity. Traditional region 1 currents occurring in cleft and outer plasma sheet almost always flow into the ionosphere in the prenoon sector and flow away from the ionosphere in the postnoon sector regardless of By polarity. Thus the midday region 1 and region 0 current system that appears at local noon is not a simple continuation of flankside region 1/region 2 current system. Midday region 1 and region 0 currents are not necessarily balanced in intensity; region 0 current intensity occasionally exceeds midday region 1 current intensity. Furthermore, intensity imbalance also appears in cleft‐associated region 1 currents; that is, region 1 current in the farside cleft from the reconnection site (“downstreamside” cleft) is larger than region 1 current in the nearside cleft (“upstreamside” cleft). On the basis of these observational facts we discuss the source mechanisms of the dayside FAC system: (1) directly coupled generation of region 0 and midday region 1 current in the cusp/mantle domains around noon and (2) generation of extra region 0 current in the tail magnetopause which is connected to the extra downstreamside cleft‐associated region 1 current.