Simultaneous Observations of Poleward‐Moving Auroral Forms at the Equatorward and Poleward Boundaries of the Auroral Oval in Antarctica

Abstract

Poleward-moving auroral form (PMAF) is a type of dayside auroral pattern. The distinguishing characteristic of a PMAF is its separation from the auroral oval and subsequent poleward motion. It has been reported and widely accepted that PMAFs occur more frequently during periods with dominant southward interplanetary magnetic field (IMF). However, most ground-based optical observations were made near magnetic latitudes of 75 • , close to the equatorward boundary of the dayside auroral oval; therefore, PMAFs occurring at the poleward boundary were likely missed easily. Using all-sky images from two stations located on the similar magnetic meridian in Antarctica at 80 • and 75 • magnetic latitude, and taking solar wind data close to the magnetosphere by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft, we demonstrate that unlike the result from prior low-latitude single-station observations, the combined observations from both stations show an insignificant difference in the PMAF occurrence rate in the northward and southward IMF conditions and no clear sign suggesting that the southward IMF or southward turning of the IMF triggers PMAFs. With good agreements between PMAF occurrence rate and the intensity of the poleward drift, we suggest that PMAFs are more likely to be plasma patches torn away from the dayside auroral oval convecting antisunward and rather than direct foot points of reconnecting flux tubes.

On the Creation, Depletion, and End of Life of Polar Cap Patches

“…Wu et al. (2020) saw a similar occurrence rate for southward and northward IMF conditions and concluded that PMAFs were more likely to be plasma patches torn away from the auroral oval than direct foot points of reconnecting flux tubes. However, for P1 and P2 the TEC data show a clear transport of lower‐latitude plasma toward the pole.…”

“…(2012) and Wu et al. (2020) showed that a notable number of PMAF‐occurrences were in the IMF B z = [‐1,1]nT interval, while 41% and 31% (in the Southern Hemisphere) of PMAFs occurred under northward conditions, respectively. Wu et al.…”

“…During the creation of the two first patches the IMF was northward, which indicates lobe reconnection. Xing et al (2012) and Wu et al (2020) showed that a notable number of PMAF-occurrences were in the IMF B z = [-1,1]nT interval, while 41% and 31% (in the Southern Hemisphere) of PMAFs occurred under northward conditions, respectively. Wu et al ( 2020) saw a similar occurrence rate for southward and northward IMF conditions and concluded that PMAFs were more likely to be plasma patches torn away from the auroral oval than direct foot points of reconnecting flux tubes.…”

Dependence of Ionospheric Responses on Solar Wind Dynamic Pressure During Geomagnetic Storms Using Global Long‐Term GNSS‐TEC Data

“…Many studies investigated the spatiotemporal variation of the auroral oval with changes in the IMF or solar wind parameters using an all‐sky camera (Drury et al., 2003; Kamide et al., 1977; Wu et al., 2020) and satellite data (Boudouridis et al., 2003; Kamide et al., 1977; Hu et al., 2017; Zhou & Tsurutani, 1999). In addition, we statistically showed the spatiotemporal change of the auroral oval during geomagnetic storms using the global GNSS‐ROTI data for 19 years.…”

Auroral Characteristics Related to AU&AL Indices

“…In this study, the processed LBHl and LBHs emission images (Wu et al, 2023) from Polar UVI from Jan 1997 to Jun 1998 are utilized. As described by Wu et al (2021), individual images have been processed to identify the auroral oval and track a cumulative energy grid in 96 magnetic local time (MLT) sectors.…”