Control of diurnal and seasonal variation of particle precipitation by regular changes of the interplanetary magnetic field

Abstract

Systematic changes of the position of the dipole axis of the Earth's magnetic field with respect to the solar axis induce distinct daily and seasonal variations of the vertical B z -component in the solarmagnetospheric coordinate system ( B ZSM ). Depending on the direction of the interplanetary magnetic field (IMF), negative B ZSM - values are produced in spring by T polarity and in autumn by A polarity, whereas in the diurnal variation lowest B ZSM -values have been calculated to occur near 23 UT for T, and near 11 UT for A polarity, respectively. In different ionospheric and geomagnetic parameters measured at high and midlatitudes increased precipitation of high energetic particles into the lower thermosphere and upper mesosphere has been detected during periods with negative B ZSM -components. The seasonal variation of the parameters investigated, with maximum values near the equinoxes, as well as a part of their diurnal variations, can thus be explained by particle precipitation being markedly controlled by the IMF sector structure.