An empirical model of the high-latitude magnetopause

A quantitative, static, empirical model of the high-latitude magnetopause is developed for GSM coordinates and parameterized by dipole tilt angle (psi), solar wind pressure, and interplanetary magnetic field (IMF) B-z. We fit 691 high-latitude magnetopause crossings by the Hawkeye 1 spacecraft to a generalized second-order surface using only crossings for which both solar wind pressure and IMF data are available. These Northern Hemisphere crossings are shown to lie within the spatial coverage of Hawkeye for different bins of psi spanning the range of -35 degrees to 35 degrees, demonstrating that the psi dependence of the crossings is not due to a bias in coverage. At high latitudes, solar wind pressure and psi are found to be of major and equal importance in modeling magnetopause position. In the Northern Hemisphere the high-latitude magnetopause is displaced outward for positive psi and inward for negative psi. Additional inward displacement of the magnetopause surface is reduced for extreme negative psi values. IMF B-z dependence is separable only after the effects of psi and pressure are removed. The radial dependence on IMF B-z weakens near the cusp and becomes stronger antisunward of the cusp, where the magnetopause is displaced outward for negative IMF B-z, and inward for positive IMF B-z. This is consistent with findings along the low-latitude flanks. Both AE and Dsr dependencies are found in the high-latitude magnetopause crossings after removing Wand pressure dependencies from the crossings. This model is only valid at high latitudes, antisunward of the cusp, out to a x(GSM) value of about -5 R-E. The psi dependence of the nose is also modeled using a subset of magnetopause crossings from Roelof and Sibeck [1993] along with Hawkeye crossings below the cusp region. For positive psi the most Sunward point of the nose is displaced below the x(GSM)-y(GSM) plane. Both the nose model and the high-latitude model are in reasonable agreement with the theoretical model of Sotirelis and Meng [1999].