Electron Temperature Variability in the Polar Cap: RISR Observations of Cold Patches, Hot Patches, and Polar Cap Arcs

Abstract:

The polar cap ionosphere is an important source of plasma for the magnetosphere due to classical polar wind outflows driven by ambipolar electric fields, and these ambipolar electric fields are controlled by the electron temperature. Therefore, magnetosphere-ionosphere coupling processes responsible for producing electron temperature variations in the polar cap will couple back on the entire magnetosphere-ionosphere system. Incoherent scatter radars can provide precise estimates of the ionospheric electron temperature. The Resolute Bay Incoherent Scatter Radar North Face (RISR-N) and Resolute Bay Incoherent Scatter Radar Canadian Face (RISR-C) have been operating in the polar cap since 2009 and 2015, respectively. Furthermore, initial demonstrations of semi-continuous observations using RISR-N were conducted in 2019 and early 2020. This study presents a survey of all of the electron temperature measurements from the RISR systems and categorizes the types of variations observed.

The electron temperature in the polar cap is strongly controlled by the solar zenith angle and photoelectron heating. While the electron temperature variations with solar zenith angle are highly predictable, the relationships between electron temperature variations and other polar cap structures are less well understood. Some observations of polar cap patches show the dense patches being significantly colder than the surrounding plasma; however, some patches can be hotter than the surrounding plasma. In addition to these hot patches, electron temperature enhancements are also observed alongside E-region density enhancements from polar cap arcs caused by particle precipitation. This study will statistically examine the solar wind and geophysical conditions associated with RISR observations of cold patches, hot patches, and polar cap arcs and use these relationships to test our current understanding of magnetosphere-ionosphere coupling in the polar cap.