Why does the subsolar magnetopause move sunward for radial interplanetary magnetic field?

This paper analyzes the distribution of different pressure components (dynamic, thermal, magnetic) in the magnetosheath along the Sun-Earth line for northward and radial interplanetary magnetic field (IMF) orientations with motivation to explain an unusual location and shape of the magnetopause often observed during the intervals of the radial IMF. The analysis employs isotropic and anisotropic MHD models, and their results are compared with the statistical processing of THEMIS observations. We have found that (1) the temperature anisotropy in the magnetosheath controls the pressure distribution near the magnetopause, and (2) the total pressure exerted on the subsolar magnetopause depends on the IMF orientation being significantly lower than the solar wind dynamic pressure for the radial IMF. The results of both MHD simulations and statistical investigations are quantitatively consistent with already published observations of the average magnetopause location as a function of the IMF orientation.