Storm-enhanced plasma density features, daytime polar cap plasmaenhancements, and their underlying plasma flows investigatedduring superstorms

摘要

This study investigates the effects of November superstorms on the daytime-eveningnorthern topside ionosphere. We utilize multi-instrument interplanetary and geomagneticdata to analyze the interplanetary shock/electric (E) field events. To assess their impact,field-aligned DMSP (Defense Meteorological Satellite Program) passes are employed. Wetracked evening storm-enhanced density (SED) features and daytime polar plasmaenhancements occurring regularly that allowed us to learn about the basic mechanismsresponsible for their development. Results show that large vertical downward plasma flowssupplied the plasma building up the SED features and polar plasma enhancements detected.These plasma formations occurred during the main phase with the forward superfountainand during a substorm with the reverse fountain. These provide observational evidence thatprimary downward plasma flows, triggered by detachment processes caused by thewestward subauroral polarization stream (SAPS) E-fields, existed and became transportedsunward. At SED latitudes, these primary downward plasma flows were intensified bythe forward superfountain when its upward plasma flow spilled over into the equatorialanomaly 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 SEDlatitudes. As the downward streaming plasma found its way to the polar cap, it resulted in thedevelopment of daytime polar plasma enhancements. Statistically, daytime polar plasmaenhancements occurred at all longitudes contradicting the myth that the North Americanregion is better suited for the development of large plasma enhancements in the polar cap.