Hydromagnetic flow around the magnetosphere

Abstract

A magnetohydrodynamic model for the interaction of the solar wind and the geomagnetic field is described, the degree to which the governing equations may be approximated by the simpler equations of the classical Chapman-Ferraro theory combined with gasdynamics is examined, and numerical results for a number of representative cases are presented. In the hydromagnetic model, the magnetosphere boundary and distant tail are represented by tangential and contact discontinuities, and the bow wave by a fast hydromagnetic shock wave. The connectivity of interplanetary and geomagnetic fields, and the asymptotic directions of the wake and shock waves at great distances from the Earth are discussed in terms of properties of these discontinuities. Detailed numerical results for the location of the bow wave, and the density, velocity, and temperature of the flow in the region between the bow wave and the magnetosphere are presented for Mach numbers 5, 8 and 12 for γ = 5 3 and 2. The calculated position of the bow wave is shown to be in good accordance with that observed in shadowgraph photographs of supersonic flow past a model magnetosphere in the Ames Supersonic Free-Flight Wind Tunnel. Results are also presented that illustrate the distortion of the interplanetary magnetic field in the region between the bow and the magnetosphere for cases in which the magnetic field in the incident stream is inclined at 45 and 90° to the free-stream direction.