On the Variation of Column Density Ratio ΣO/N₂ in the Upper Atmosphere Using Principal Component Analysis in 2‐Dimensional Images

Abstract

The variability of the thermosphere on a daily basis is influenced by a variety of factors, including solar, geomagnetic, and meteorological drivers. The column density ratio of atomic oxygen to molecular nitrogen (ΣO/N2) is a useful parameter for quantifying this variability, and has been shown to closely correspond to F‐region electron density, total electron content, and upper atmospheric transport. Despite the significance of the ΣO/N2, the relative contributions of these drivers to thermospheric variability are not well understood. In order to shed light on this issue, principal component analysis was performed in this study to distinguish and rank the various sources of variability in the ΣO/N2. The analysis was based on the ΣO/N2 data from the Global‐scale Observations of the Limb and Disk mission from days 81–135 of 2020. The resulting two‐dimensional eigen spatial patterns reveal the dominant variabilities during the specified period. The first six principal components are reported and associated with the major drivers through their spatial and temporal features. Geomagnetic storms, interhemispheric transport, atmospheric tides, and planetary waves were identified as the drivers of the first, second, third, and fifth components, respectively. The order of these components highlights that geomagnetic activity is the dominant source of daily variability in the ΣO/N2, followed by interhemispheric transport and meteorological drivers from the lower atmosphere.

Thermospheric Responses to the 3 and 4 November 2021 Geomagnetic Storm During the Main and Recovery Phases as Observed by NASA's GOLD and ICON Missions

“…One of the key state parameters that ICON measures is wind profiles spanning 90-300 km at low and middle latitudes (Englert et al, 2023;Harding et al, 2021;Makela et al, 2021), and GOLD provides unparalleled synoptic observations of disk O/N 2 and temperatures (Eastes et al, 2020). The two missions have been revolutionizing the understanding of the ionosphere-thermosphere dynamics during solar and geomagnetically active and quiet times (e.g., Cai et al, 2023;Eastes et al, 2020;England et al, 2020;Gan et al, 2020aGan et al, , 2020bGan et al, , 2023aGan et al, , 2023bGoel et al, 2023;Immel et al, 2023;Laskar et al, 2022;McGinness et al, 2023;Oberheide et al, 2020). The current investigation is motivated by a previous study- Gan et al (2020a)-that reported the first observational changes in atomic oxygen (OI 135.6 nm brightness was used as a proxy) from the GOLD mission during the 5 November 2018 CME (Coronal Mass Ejection) storm.…”