Magnetopause inflation under radial IMF: Comparison of models

The solar wind with the radial interplanetary magnetic field (IMF) flowing around the Earth's magnetosphere can result in significant decrease of a total pressure in the magnetosheath that was directly observed by Time History of Events and Macroscale Interactions during Substorms satellites. Observations also showed that the dayside magnetosphere enlarged and the magnetopause inflated far away from the Earth that differs from the classical hydrodynamic case. Full understanding of the magnetosphere interaction with such “radial” flow, is far from completeness. One of the reasons is a quantitative uncertainty in description of this effect. We have performed a comparative analysis of 14 magnetopause models in order to estimate their prediction capabilities under various solar wind pressures and in particular under very low pressures during the time intervals of quasi-radial IMF orientation. We have found that only 4 out of 14 models allow predicting the magnetopause under extremely low pressures and, hence, can be useful for quantitative estimation of the magnetopause expansion under quasi-radial IMF orientation. Those models are characterized by relatively large power index α in the pressure balance; that is, α = 1/5.2 ≈ 0.192 for 3 out of 4 models.