Dawn‐dusk profile of field‐aligned currents on May 11, 1999: A Familiar pattern driven by an unusual cause

On May 11, 1999, when the solar wind almost disappeared, the DMSP‐F13 satellite observed two field‐aligned current (FAC) sheets on both dawn and dusk sides. The dawnside FACs are identified as conventional region 1 (R1) and region 2 (R2) currents. The duskside FACs are collocated with intense polar‐rain precipitation and are identified as midday region 1 and region 0 currents. Whereas the positive IMF B Y observed explains the duskward shift/extension of those midday current systems, the extent of the distortion was unusual. It is inferred that the magnetospheric configuration was more axisymmetrical because of extremely low solar‐wind dynamic pressure, and therefore the reconnection took place farther away from the midday sector. Conventional R1 and R2 currents as well as boundary layer‐type precipitation were nearly absent at dusk, suggesting that the viscous interaction did not operate at least observably on the dusk side in the present event.