Timescales of Birkeland Currents Driven by the IMF

We obtain current densities from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE), alongside B_y and B_z from the Interplanetary Magnetic Field (IMF) for March 2010. For each AMPERE spatial coordinate, we cross-correlate current density with B_y and B_z, finding the maximum correlation for lags up to 360 min. The patterns of maximum correlation contain large-scale structures consistent with the literature. For the correlation with B_y, the lags on the dayside are 10 min at high latitudes but up to 240 min at lower latitudes. Lags on the nightside are 90–150 min. For B_z, the shortest lags on the dayside are 10–20 min; on the equatorward edge of the current oval, 60–90 min; and on the nightside, predominantly 90–150 min. This novel approach enables us to see statistically the timescales on which information is electrodynamically communicated to the ionosphere after magnetic field lines reconnect on the dayside and nightside.