IMF B/sub y/-dependent plasma flow and Birkeland currents in the dayside magnetosphere: 2. A global model for northward and southward IMF

This paper extends to all interplanetary magnetic field (IMF) orientations the qualitative convection pattern presented by Burch et al. (this issue), containing viscous, merging, and lobe cells driven, respectively, by diffusion or other quasi-viscous processes, merging of interplanetary fields with closed dayside field lines, and merging of interplanetary fields with open tail lobe field lines. The model is based on the antiparallel merging hypothesis of Crooker (1979a) with the addition of small but finite cells driven by quasi-viscous processes on the dawn and dusk edges of the polar cap. The data and model presented by Burch et al. pertained to southward IMF conditions. This paper generalizes that model and proposes a qualitative dependence of the three types of convection cells on the x, y, and z components of the IMF. For example, the lobe cell should be enhanced in the northern hemisphere if B/sub x/ < 0 and in the southern for B/sub x/ > 0, and, for a given B/sub x/ and B/sub z/, should be larger as Vertical Bar B/sub y/ Vertical Bar increases. For northward IMF, the merging cell disappears, leaving only the lobe cell in as a smaller polar cap. If the y component of the IMF (B/sub y/) is small, we infer the four-cell pattern of Burke et al. (1979), with two counter-rotating lobe cells having sunward flow in the central polar cap and tailward flow on the flanks