ИСТИНА

Interaction of the solar wind with the magnetosphere is going through the magnetosheath, so that the magnetosheath total pressure controls the magnetopause location. We have analyzed THEMIS data to compare the magnetosheath pressures and magnetopause locations for radial and nominal Parker-spiral orientations of interplanetary magnetic field (IMF) during quiet geomagnetic activity and nearly constant solar wind dynamic pressure. For radial IMF, we have found the magnetopause to be far beyond of its expected location, while its location for Parker-spiral IMF was in a good agreement with a model. The expanded magnetopause states can persist several hours, just as long as the quasi-radial IMF conditions, indicating steady-state situations. The magnetopause expansions result from dramatic decreases in the total pressure of the high- magnetosheath, which we term the low-pressure magnetosheath (LPM) mode. We show and quantify decreases in the magnetosheath pressure induced by IMF rotations to the quasi-radial orientation rather than by decreases in the solar wind dynamic pressure. In the LPM mode, the minimum value for the total pressure observed by THEMIS in the magnetosheath adjacent to the magnetopause was 0.16 nPa and the fraction of the solar wind pressure applied to the magnetopause was 0.2 that is extremely smaller than theoretical prediction of 0.881. The equilibrium location of the distant magnetopause was modulated by a nearly continuous wavy motion over a wide range of time and space scales.