Evolution of the subauroral polarization stream oscillations during the severe geomagnetic storm on 20 November 2003

The SAPS oscillations (SAPSOs) occurred during the main phase of the magnetic storm when the y component of the southward interplanetary magnetic field (IMF B-Y) turned from positive to negative. The SAPSOs were first observed in the premidnight sector and propagated toward the dusk sector.

The formation and evolution of SAPSO corresponded well with the plasma sheet ions injection and precipitation, indicating that the SAPSOs are possibly generated by the interaction between the hot plasma sheet and the cold plasmasphere under particular conditions (e.g., change of the polarity of IMF B-Y accompanied with a sudden enhancement of plasma sheet ion density). The hemispheric asymmetry of the SAPS channels is suggested to be related to the hemispheric differences in the ionospheric plasma condition and the ionospheric convection.