A quantitative model for the potential resulting from reconnection with an arbitrary interplanetary magnetic field

Abstract

A three-dimensional model is utilized to derive the electric potential induced across the magnetosphere by reconnection between the geomagnetic field and an arbitrary interplanetary magnetic field. Assumptions that the magnetosheath flow is uniform and that reconnection is not limited by processes occurring at the magnetopause are made so that the model calculation provides an upper limit to the magnetospheric potential produced by reconnection. The magnitude of the polar cap ionospheric electric field computed from this model is larger than that measured on balloons by an average factor of about 3, and the model reproduces the temporal variations of the experimental data. Some magnetospheric properties related to the magnetopause reconnection line and potential are discussed as a first suggestion toward using the model in studies of relevant magnetospheric problems. The model potential induced across the magnetosphere becomes less dependent on the direction of the interplanetary magnetic field as the strength of its transverse component increases. Thus a reduced correlation between magnetospheric phenomena and the southward component of the interplanetary field should exist when the transverse interplanetary field component exceeds about 8 γ. Observed dependences of the polar cap ionospheric current system on By are explained by the model, and similar variations with Bx are predicted. Graphs of the model potential as functions of the interplanetary magnetic field components are given as an aid in its application to other problems.