Storm‐enhanced plasma density features, daytime polar cap plasma enhancements, and their underlying plasma flows investigated during superstorms

This study investigates the effects of November superstorms on the daytime-evening northern topside ionosphere. We utilize multi-instrument interplanetary and geomagnetic data to analyze the interplanetary shock/electric (E) field events. To assess their impact, field-aligned DMSP (Defense Meteorological Satellite Program) passes are employed. We tracked evening storm-enhanced density (SED) features and daytime polar plasma enhancements occurring regularly that allowed us to learn about the basic mechanisms responsible for their development. Results show that large vertical downward plasma flows supplied the plasma building up the SED features and polar plasma enhancements detected. These plasma formations occurred during the main phase with the forward superfountain and during a sub-storm with the reverse fountain. These provide observational evidence that primary downward plasma flows, triggered by detachment processes caused by the westward sub-auroral polarization stream (SAPS) E-fields, existed and became transported sunward. At SED-latitudes, these primary downward plasma flows were intensified by the forward superfountain when its upward plasma flow spilled over into the equatorial anomaly and cascaded down the magnetic field lines. When the reverse fountain was active, such intensification was not available to the primary downward plasma flows at SED-latitudes. As the downward streaming plasma found its way to the polar cap, it resulted in the development of daytime polar plasma enhancements. Statistically, daytime polar plasma enhancements occurred at all longitudes contradicting the myth that the North American region is better suited for the development of large plasma enhancements in the polar cap.