Seasonal differences in ionospheric current rise and decay times

Abstract:

We investigate how different seasonal conditions are associated with differences in the ionospheric response to the same magnetospheric and solar wind drivers. In particular, we use ground magnetometer data, made available by SuperMAG, to derive equivalent current maps, and analyze how these currents respond to 1) Substorm onsets, and 2) rapid changes in the interplanetary magnetic field (IMF). We find that at substorm onset, determined from global auroral imaging, the average ionospheric current starts to increase almost immediately in the winter hemisphere, while a several minutes delay is observed in the summer hemisphere. In the winter hemisphere, the increase in current is on average larger than in the summer hemisphere during the substorm growth phase. During substorm recovery, the current decays more rapidly in the winter hemisphere, compared to the summer hemisphere. This is consistent with some earlier studies that show that the ionospheric convection changes more slowly when the ionospheric conductance is high.