Magnetic field orientation effects on the standoff distance of Earth's bow shock

Three‐dimensional, global MHD simulations of solar wind flow onto a prescribed magnetopause obstacle are used to show that a bow shock's nose location a s and the relative subsolar magnetosheath thickness Δ ms / a mp are strong functions of the IMF cone angle θ (between v sw and B sw ) and the Alfven Mach number M A For a given M A the shock is more distant for higher θ (restricted to the interval 0–90° by symmetries), while a s / a mp and Δ ms / a mp increase with decreasing M A for θ ≳ 20° but decrease with decreasing M A for θ ∼ 0°. Large differences in Δ ms / a mp are predicted between θ = 0° and 90° at low M A , with smaller differences remaining even at M A ∼ 10. The θ = 0° results confirm and extend the previous work of Spreiter and Rizzi [1974]. The simulations show that successful models for the subsolar shock location cannot subsume the dependences on M A and θ into a sole dependence on M ms . Instead, they confirm a recent prediction [ Cairns and Grabbe , 1994] that a s / a mp and Δ ms / a mp should depend strongly on θ and M A for M A ≲ 10 (as well as on other MHD variables). Detailed comparisons between theory and data remain to be done. However, preliminary comparisons show good agreement, with distant shock locations found for low M A and large θ ≳ 45° and closer locations found for θ ≲ 20° even at M A ∼ 8.