Ground Magnetic Perturbations in the Polar Cap and Cleft: Structure and Dynamics of Ionospheric Currents

Abstract

Ground magnetic perturbations in the polar cap and cleft are very closely related to variations in the solar wind parameters through the magnetic field-lines which map to the boundary layers of the magnetosphere. The magnetic variations in the polar cap respond almost immediately to variations in the interplanetary magnetic field (IMF), although it takes some time for the large-scale ionospheric currents to adapt to a sudden change in the IMF. Dense arrays of magnetometers provide a possibility to resolve the structure of the ionospheric currents, which are very complex around magnetic local noon. The cleft is thought to map to the low-latitude boundary layer which is generally located on closed field-lines. In this region small-scale features known as magnetic impulse events have been shown to correspond to tailward moving ionospheric current vortices which are probably related to sudden changes in the solar wind dynamic pressure. But also other magnetopause processes may have ionospheric signatures which are seen in the ground magnetic records.