Magnetospheric cross-field currents during the January 6–7, 2011 high-speed stream-driven interval

The cross-field current systems within a global, coupled geospace simulation of the January 6, 2011 high-speed stream-driven interval are analyzed to understand the flow and partitioning of energy within the magnetosphere. Even though this is a small storm with a minimum Dst of −41 nT, it is shown that the time-dependence of current system locations is very similar to that from a much larger storm (minimum Dst of −230 nT) driven by an interplanetary coronal mass ejection. That is, during the early part of the main phase, the tail current inner edge moves Earthward inside of geosynchronous orbit, but then retreats during the later part of the main phase, and by the peak of the storm interval, the ring/tail boundary is beyond L=10 in the nightside magnetosphere. It is also seen that a banana current (the part of the partial ring current that does not close through the ionosphere but rather with itself by flowing around the pressure peak entirely on the nightside) accounts for nearly all of the eastward current and the innermost portion of the westward current in the equatorial plane throughout the storm main phase interval.