The Effects of IMF B_y on the Middle Thermosphere During a Geomagnetically “Quiet” Period at Solar Minimum

Abstract

Numerical simulations using the National Center for Atmospheric Research (NCAR) thermosphere‐ionosphere‐electrodynamics general circulation model (TIE‐GCM) are performed to elucidate the effects of the interplanetary magnetic field (IMF) on the middle thermosphere composition during a “geomagnetically quiet” period from the day of year (DOY) 110–111 in 2019 (when the Auroral electrojet (AE) index never exceeded 300 nT and the Kp never exceeded 2). In particular, this paper aims to examine how the Global‐scale Observations of the Limb and Disk (GOLD) mission observed daytime thermospheric O and N2 column density ratio (∑O/N2) depletion at mid‐latitudes originated under such a “geomagnetically quiet” condition. A comparison of electric potential, Joule heating rate per unit mass, ion velocity, neutral temperature and winds in the middle thermosphere (∼160 km) between real IMF and without the IMF east‐west component (By) indicates that a By dominant condition can enhance their strengths under this “geomagnetically quiet” condition. Consequently, ∑O/N2 depletion with a stronger magnitude (30% compared with ∼8% without By) and larger disturbed area was introduced in the post‐midnight sector at high‐latitudes due to strong and localized upwelling associated with the enhanced Joule heating rate per unit mass. The ∑O/N2 depletion was transported equatorward and corotated from local post‐midnight to early morning, and was observed by GOLD at middle latitudes during daytime.

Investigation of the ΣO/N2 Depletion With Latitudinally Tilted Equatorward Boundary Observed by GOLD During the Geomagnetic Storm on April 20, 2020

“…This depletion region is different from the depletion regions seen in previous studies utilizing GOLD observation. For example, the depletions reported in Cai et al (2020) and Cai, Burns, Wang, Qian, Pedatella, et al (2021), Cai et al (2022) do not exhibit a tilted latitudinal structure (i.e., they almost parallel to longitude axis).…”

“…(2021), Cai et al. (2022) do not exhibit a tilted latitudinal structure (i.e., they almost parallel to longitude axis).…”

“…The recently launched Global-scale Observations of the Limb and Disk (GOLD) mission in geostationary orbit provides two-dimensional (2D) synoptic images at the same universal time (UT) range every day, which gives us a great opportunity to study the response of the thermospheric composition 2D structures to geomagnetic disturbances. Although there are already several studies focusing on the 2D ∑O/N 2 responses to geomagnetic disturbances based on GOLD observations (Cai, Burns, Wang, Qian, Solomon, et al, 2021;Cai, Burns, Wang, Qian, Pedatella, et al, 2021;Cai et al, 2020Cai et al, , 2022, none of them provide detailed investigations on ∑O/N 2 depletion structures during the storm. Furthermore, as mentioned earlier, the horizontal advection dominates the behavior of ∑O/N 2 disturbance when it is transported to mid-low latitudes, suggesting the important role of the horizontal winds.…”

Hemispherically Asymmetric Evolution of Nighttime Ionospheric Equatorial Ionization Anomaly in the American Longitude Sector

“…GOLD provides Far Ultraviolet images of the same region (over 120°longitude × 140°latitude) in the same UT range every day. It uses two Channels (Channel A and B) during the daytime to observe Earth's airglow emission from 134 to ∼162 nm with a spectral resolution of 0.2 nm (Eastes et al., 2017, 2020), which are utilized to derive thermospheric composition and temperature (Cai, Wang, et al., 2022; Krier et al., 2021; Qian et al., 2022). During the nighttime, it observes the OI 135.6 nm with a spectral resolution of 0.4 nm (Eastes et al., 2019).…”

Mid‐Latitude Ionospheric Response to a Weak Geomagnetic Activity Event During Solar Minimum

“…∑O/N 2 is derived from OI 135.6 nm and the N 2 LBH brightness during the daytime. For the daytime mode, GOLD imager scans the full disk with a 30‐min temporal resolution between 6:10 and 22:40 UT and from 120°W to 30°E in longitude and from 70°S to 70°N in latitude (Cai, Wang, et al., 2022; Qian et al., 2022) The Northern Hemisphere ∑O/N 2 with 1° × 1° spatial resolution is utilized in this study. Small‐scale variations are removed by a 5° × 5° moving window in latitude and longitude.…”