Substorm Impact on Dayside Ionospheric Currents

Abstract

Ionospheric dayside dynamics is strongly controlled by the interaction between the Interplanetary Magnetic Field (IMF) and the Earth's magnetic field near the dayside magnetopause, while nightside ionospheric dynamics depends mainly on magnetotail activity. However, we know little about the influence of magnetotail activity on the dayside ionospheric dynamics. We investigate this by performing superposed epoch analyses of ground magnetic field data for substorms occurring during northward IMF. In such substorms, dayside reconnection is minimized, allowing us to separate the effects of the magnetotail activity on the dayside current system. We find that as nightside activity elevates, the dayside ionospheric current elevates. Our analyses indicate that the lobe cells are less distinct before onset than during non-substorm northward IMF conditions. They become more pronounced after onset, possibly due to magnetospheric reconfiguration or a remote effect of the nightside current. We discuss possible mechanisms that may explain our observations.