An empirical model of the high‐latitude magnetopause

Abstract

A quantitative, static, empirical model of the high‐latitude magnetopause is developed for GSM coordinates and parameterized by dipole tilt angle (ψ), solar wind pressure, and interplanetary magnetic field (IMF) Bz. 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 ψ spanning the range of −35° to 35°, demonstrating that the independence of the crossings is not due to a bias in coverage. At high latitudes, solar wind pressure and ψ 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 ψ and inward for negative ψ. Additional inward displacement of the magnetopause surface is reduced for extreme negative ψ values. IMF Bz dependence is separable only after the effects of ψ and pressure are removed. The radial dependence on IMF Bz weakens near the cusp and becomes stronger antisunward of the cusp, where the magnetopause is displaced outward for negative IMF Bz, and inward for positive IMF Bz. This is consistent with findings along the low‐latitude flanks. Both AE and Dst dependencies are found in the high‐latitude magnetopause crossings after removing ψ and pressure dependencies from the crossings. This model is only valid at high latitudes, antisunward of the cusp, out to a xGSM value of about −5 Rε. The ψ 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 ψ the most Sunward point of the nose is displaced below the xGSM‐yGSM plane. Both the nose model and the high‐latitude model are in reasonable agreement with the theoretical model of Sotirelis and Meng [1999].