Magnetotail Flux Accumulation Leads to Substorm Current Wedge Formation: A Case Study

Reconnection‐generated earthward flows, magnetic field dipolarizations, and auroral expansions are related to substorm current wedge (SCW) development. It has been suggested that field‐aligned currents (FACs) within the SCW can be generated by flow vortices, pressure gradients, or both. Observations related to these generation mechanisms differ from one event to another, due to their different locations relative to SCW's central meridian and timing relative to the SCW's evolutionary state. A pattern of in situ observations consistent with these generation mechanisms has yet to emerge. Obtaining such a pattern of in situ observations relies on the satellite locations relative to the FAC driver regions, which are hard to determine because coincident magnetotail observations are sparse. To solve this problem, an SCW inversion technique was used to model the FAC locations and determine the connections between magnetospheric and ionospheric phenomena. Using this technique, the magnetic flux, a parameter that is relatively insensitive to FAC locations, was analyzed during an isolated substorm on February 13, 2008. We compared the temporal variations of the accumulated flux that caused magnetic dipolarization in the SCW and the flux within the auroral poleward boundary. We found them to be in good agreement with the flux transported by earthward flows. This agreement suggests that the accumulation of the magnetic flux leads to the generation of the SCW, causing magnetic dipolarization and auroral poleward expansion. The amount of accumulated flux was found to be positively correlated with the amplitudes of these substorm‐related phenomena.