K. Kabin

In this paper we present results concerning periods and polarizations of cold plasma ultra-low frequency (ULF) guided Alfvén waves in a non-axisymmetric geomagnetic field. The background geomagnetic field is approximated by a compressed dipole for which we propose a simple description in terms of Euler potentials. This study is motivated by the problem of outer-radiation belt electron acceleration by ULF waves, for which the polarization of the wave is of paramount importance. We consider an approximation appropriate to decoupled Alfvénic waves and find that the polarization of the waves can change significantly with local time. Therefore, the ULF wave's contribution to the MeV electron energization process can be localized in space.

In this paper we investigate the effect of changes in the interplanetary magnetic field (IMF), solar wind dynamic pressure, and dipole tilt angle on the position of the ionospheric projection of the open‐closed field line boundary (OCB) in a magnetohydrodynamic (MHD) model. We carry out a large number of steady state global MHD simulations in order to parameterize the OCB as a function of the solar wind B_y and B_z which we find to have the largest effect on the OCB location. We interpolate between the values produced by the simulations, which allows us to evaluate the location of the OCB projection into the ionosphere for any values of ∣B_y∣ < 10 nT and ∣B_z∣ < 10 nT. It is found that, particularly on the nightside, the OCB position is very sensitive to changes in the northward IMF component B_z, but it is much less sensitive to changes in B_z when it is southward. The response of the OCB location to changes in B_y also depends greatly on whether B_z is northward or southward, being much larger in situations in which B_z > 0 nT. We also find that the polar cap area increases with the increasing solar wind dynamic pressure. The B_x component of the IMF and the dipole tilt angle are found to have relatively small effects on the location of the OCB.