The Locations and Shapes of Jupiter’s Bow Shock and Magnetopause

Abstract

The shape and location of the Jovian bow shock and magnetopause have been studied by using magnetic field observations and global magnetohydrodynamic (MHD) simulations. MHD simulations in which the interplanetary magnetic field (IMF) was set to zero were used to define the boundary shapes and positions and how they depend on solar wind dynamic pressure. Polynomial fits to the simulated boundaries along with spacecraft observations were used to determine the probability of a given position being outside of the bow shock or inside of the magnetopause. The magnetopause and possibly the bow shock have two preferred locations, one representing a compressed magnetosphere and the other an expanded magnetosphere. Variations in the solar wind parameters near Jupiter also show a bimodal distribution but the changes in the solar wind dynamic pressure are not sufficient to account for the observed bimodal distribution of observed magnetopause positions. Internal pressure changes at Jupiter are required. The interplanetary magnetic field also influences the location and shape of the boundaries. In particular, when the IMF is in the By direction or northward magnetopause reconnection acts to reduce polar flattening. Higher internal pressure at dusk leads to a dawn‐dusk asymmetry in the magnetopause position with the boundary being farther from Jupiter on the dusk side. For all the simulations the ratio of the bow shock stand‐off distance to that of the magnetopause was less than that at the Earth.