The role of diffuse electron precipitation in the formation of subauroral polarization streams

Diffuse precipitation is derived from the distribution of drifting electrons. SAPS manifest themselves as a separate mesoscale flow channel in the duskside ionosphere, which gradually merges with the primary auroral convection toward dayside as the equatorward auroral boundary approaches the poleward Region-2 field-aligned currents (FACs) boundary.

SAPS expand to lower latitudes and toward the nightside during the main phase of a geomagnetic storm, associated with magnetotail earthward plasma flows building up the ring current and intensifying Region-2 FACs and electron precipitation. SAPS shrink poleward and sunward as the interplanetary magnetic field turns northward. When diffuse precipitation is turned off in a controlled MAGE simulation, ring current and duskside Region-2 FACs become weaker, but subauroral zonal ion drifts are still comparable to auroral convection.