Timescales of Birkeland currents in geomagnetic storms

Abstract:

Effective forecasting of space weather conditions allows us to better predict geomagnetic effects on Earth. However, a key part of this is knowledge of the timescales on which solar wind-magnetosphere-ionosphere coupling operates, especially during geomagnetic storms. To this end, we use the Spatial Information from Distributed Exogenous Regression (SPIDER) technique to investigate the timescales of Birkeland current driving during geomagnetic storms. For each AMPERE spatial co-ordinate, we cross-correlate current density with IMF and SuperMAG-derived geomagnetic indices, finding the maximum correlation for lags up to 360 minutes. The patterns of maximum correlation contain large-scale structures which reveal things about the behaviour of the system during these storms.

This novel approach enables us to see statistically the timescales on which information is electrodynamically communicated to the ionosphere after magnetic field lines reconnect at the magnetopause and in the magnetotail during the geomagnetic storm in question. We select a geomagnetic storm which was preceded by a long period of northward IMF for our case study for future comparisons with Gorgon and SuperMAG.