Coupling of IMF BY variations into the polar ionospheres through interplanetary field‐aligned currents

Abstract

Studies of the correlation between the geomagnetic fields recorded at high‐latitude observatories and the interplanetary magnetic field (IMF) observed from the IMP 8 satellite in the solar wind have indicated that variations in the IMF BY component may generate perturbations of similar appearance in the geomagnetic north (H) components observed in the noon sector of the dayside polar cap. During southward interplanetary field conditions (IMF BZ < 0) these perturbations are observed to progress poleward from the cusp region across a large fraction of the dayside polar cap, changing only slightly in shapes and amplitudes. These progressing geomagnetic variations are interpreted as the footprints of the variable IMF BY component present in the solar wind volume which is magnetically connected to the polar cap ionosphere. It is suggested in this work that both the IMF BY variations and the corresponding variations in the H(ground) components are related to interplanetary field‐aligned currents. The “open” magnetospheric topology, resulting from the merging of the geomagnetic field and the interplanetary field during southward interplanetary field conditions, allows these interplanetary currents to flow along the merged field lines to the northern and southern polar cap ionospheres. Here they generate the convection‐related Hall currents responsible for the observed geomagnetic perturbations. The closure from one polar cap to the other can be partly in the form of ionospheric Pedersen currents and partly in the form of field‐aligned currents along closed field lines in the inner magnetosphere.