Relationship between four‐cell and distorted two‐cell convection patterns during northward IMF

Abstract

Four‐cell convection pattern in the ionosphere during a northward IMF (interplanetary magnetic field) was widely accepted until it was challenged by the distorted two‐cell convection pattern proposed by Heppner and Maynard [1987]. We propose that a four‐cell convection pattern, imposed on the magnetosphere by the solar wind, can be distorted into a wrapped two‐cell pattern by the nonuniform and anisotropic conductance in the ionosphere. This is demonstrated by extending the magnetosphere‐ionosphere coupling model [Kan et al., 1988] to the northward IMF condition. The resulting wrapped two‐cell patterns for positive and negative IMF By are similar to the empirical two‐cell patterns obtained by Heppner and Maynard [1987]. The distributions of the resulting field‐aligned currents are also characteristically consistent with the observed current distributions, including the NBZ currents, during northward IMF.