The Influence of the Solar Sector Angle on the Ionosphere

Abstract:

Undulations of the heliospheric current sheet result in identifiable sectors at Earth where the interplanetary magnetic field (IMF) is directed predominantly toward or away from the Sun. When the IMF is directed toward the Sun magnetic reconnection results in open magnetic field lines in the northern polar cap that are directed upstream into the solar wind, providing a path of direct access for solar wind plasma into the northern polar cap and producing polar rain. At the same time, the reconnected field lines threading the southern polar cap are directed downstream, draping along the magnetotail and leading to low particle fluxes precipitating into the southern polar cap. The magnetic field asymmetry arising from a strong radial IMF component results in asymmetric particle fluxes in the north and south polar caps. At times, a very clear correlation exists between the number of echoes recorded by the Super Dual Auroral Radar Network (SuperDARN) and the orientation of IMF in the solar sector. The polar cap that is connected upstream produces fewer ionospheric and ground echoes for the SuperDARN radars in that hemisphere. The echo occurrence is opposite in the north and in the south, and the high or low echo occurrence persists through the solar sector. The presence or lack of polar rain precipitation is expected to alter the ionospheric density profile and lead to different propagation of the radio waves through the ionosphere. Changes in tropospheric weather circulation have been linked to the passage of a solar sector boundary at Earth, and this direct solar-terrestrial influence at ionospheric altitudes may prove to be essential in understanding interplanetary influences on the troposphere.