Relationship of topside ionospheric ion outflows to auroral forms and precipitation, plasma waves, and convection observed by Polar

Abstract

The POLAR satellite often observes upflowing ionospheric ions (UFIs) in and near the auroral oval on southern perigee (∼5000 km altitude) passes. We present the UFI features observed by the thermal ion dynamics experiment (TIDE) and the toroidal imaging mass angle spectrograph (TIMAS) in the dusk‐dawn sector under two different geomagnetic activity conditions in order to elicit their relationships with auroral forms, wave emissions, and convection pattern from additional POLAR instruments. During the active interval, the ultraviolet imager (UVI) observed a bright discrete aurora on the duskside after the substorm onset and then observed a small isolated aurora form and diffuse auroras on the dawnside during the recovery phase. The UFIs showed clear conic distributions when the plasma wave instrument (PWI) detected strong broadband wave emissions below ∼ 10 kHz, while no significant auroral activities were observed by UVI. At higher latitudes, the low‐energy UFI conies gradually changed to the polar wind component with decreasing intensity of the broadband emissions. V‐shaped auroral kilometric radiation (AKR) signatures observed above ∼200 kHz by PWI coincided with the region where the discrete aurora and the UFI beams were detected. The latitude of these features was lower than that of the UFI conies. During the observations of the UFI beams and conies, the lower‐frequency fluctuations observed by the electric field instrument were also enhanced, and the convection directions exhibited large fluctuations. It is evident that large electrostatic potential drops produced the precipitating electrons and discrete auroras, the UFI beams, and the AKR, which is also supported by the energetic plasma data from HYDRA. Since the intense broadband emissions were also observed with the UFIs, the ionospheric ions could be energized transversely before or during the parallel acceleration due to the potential drops.