Do the Throat Auroras Create Polar Cap Patches?

Abstract

Throat auroras and polar cap patches are common phenomena in the polar ionosphere resulting from solar wind-magnetosphere-ionosphere coupling. The throat aurora is a discrete aurora that is associated with localized magnetopause indentations (Han, 2019). It is usually located equatorward of the cusp aurora oval near magnetic noon, oriented in the south-north direction (Han et al., 2015) and is more frequently observed under radial interplanetary magnetic field (IMF, Bx-dominated conditions) (e.g., Han et al., 2017;Rodriguez et al., 2012). Han et al. (2016) indicated that throat aurora is an ionospheric feature in which magnetosheath particles enter the magnetosphere along open magnetic field lines, based on data from ground-based all-sky imagers (ASIs) and Magnetospheric Multiscale (MMS) satellites. Throat auroras are also observed to be accompanied by Joule heating and ion upflows, based on data from a European Incoherent Scatter (EISCAT) radar experiment (Han et al., 2019), which supports throat aurora being associated with magnetopause reconnection.The polar cap patch is another common phenomenon in the dayside ionosphere polar regions. It is also associated with transient dayside reconnection (e.g., Carlson et al., 2004;Lockwood & Carlson, 1992;Zhang et al., 2011Zhang et al., , 2013. A patch is an island of high-density F region ionospheric plasma with a typical size of

Multi‐Instrument Observations of the Evolution of Polar Cap Patches Associated With Flow Shears and Particle Precipitation

“…There were also several auroral arcs on the nightside from 1404 UT observed by the RSB ASI at 630.0 nm band. Previous studies have suggested that polar cap patches are related to dayside auroral structures like poleward moving auroral form (PMAF) (Lorentzen et al., 2010; Nishimura et al., 2014; Zhang et al., 2010) and throat aurora (Zhang et al., 2023). Our auroral arc was accompanied by electron density enhancement and soft‐electron precipitation (Michell et al., 2008), but the relationships between polar cap patches and auroral arcs in the polar cap needs to be investigated in future work.…”

“…The cold patches are related to solar activity and found in the central polar cap (D. Zhang et al, 2021Zhang et al, , 2022. The hot patches are found close to the auroral oval, associated with strong auroral emissions, ion upflows, and flow shears (e.g., Lorentzen et al, 2010;Ma et al, 2023;Nishimura et al, 2014;Zhang et al, 2023). The electron temperature of a hot patch may decrease to the same level as the ion temperature when the particle precipitation decreases, that is, it becomes a cold patch (Ma et al, 2023), which was obtained by analyzing two different patch events, rather than a complete evolution process of a patch.…”