ИСТИНА

We use a term of “low-pressure magnetosheath mode” or LPM mode describing specific condition of the solar wind flow around the Earth’s magnetosphere, which is formed under the radial IMF and differs from the classical hydrodynamic approach. The LPM mode means that the fraction of the SW pressure applied to the magnetopause, the ratio K, is considerably smaller than theoretical prediction of 0.881. We discuss observational aspects of the LPM problem using multi-point THEMIS observations during 2007-2008. We studied time intervals of long-lasting radial IMF with duration of more than 1 hour. In most cases the prominent LPM mode (K<0.6) was accompanied by enlarging of the dayside magnetosphere and intense generation of small-scale magnetosheath plasma jets that resulted in a restriction of obvious observation of the LPM mode. We concern following important issues: 1) an instrumental effect, i.e. the accuracy of ratio K calculation can be greatly affected by THEMIS calibration; 2) time propagation of radial IMF structures observed far upstream often differs from generally used values from OMNI database; 3) solar wind monitor near the Earth is preferred to use; 4) simultaneous observations of the LPM mode with the magnetopause appearing in the far magnetosheath or foreshock; 5) differences in the flank and subsolar magnetosheath. Various solar wind parameters were studied as a driver of the LPM mode.