Field aligned currents in the high latitude, high altitude magnetosphere: POLAR initial results

Magnetic field measurements obtained by the POLAR spacecraft are used to map out the region 1 and region 2 field-aligned current systems in the dayside hemisphere at radial distances of close to 8 Earth radii above the northern polar cap. The extrapolated invariant latitude of these currents is quite variable. The equatorward edge of the region 1 system ranges from 73 to 83° degrees invariant latitude. The sense of both systems reverses across noon as expected. The strength of the currents also varies, averaging about 0.03 A/m for the region 1 currents and 0.01 A/m for the region 2 currents. Over the dayside hemisphere this amounts to about 1.5 million amps flowing down and up the field lines in the region 1 system and about 0.5 million amps in the region 2 system. These numbers and the behavior of the current are quite consistent with low-altitude observations.