Nightside dynamics influence on the dayside ionospheric current

The main driver of the ionospheric dayside dynamics is the interaction between the interplanetary magnetic field (IMF) and the Earth’s magnetic field near the dayside magnetopause, while magnetotail activities control the nightside ionospheric dynamics. In spite of that, our knowledge about the influence of magnetotail activity on the dayside ionospheric dynamics and vice versa is limited. We investigate the nightside influence on the dayside ionospheric current by performing superposed epoch analyses of ground magnetic field data for northward IMF substorms. Such substorms encounter minimal influence of the dayside reconnection, granting an opportunity to isolate the effects of magnetotail activity on the dayside current system. Our analyses indicate that as nightside activity elevates, the dayside ionospheric current changes. We also find that lobe reconnection is weaker before substorm onset than what is expected for northward IMF conditions and then increases after onset, possibly due to reconfiguration of the magnetosphere. We present three possible mechanisms that can explain our observations.