Day-to-day variability in thermospheric composition is driven by solar, geomagnetic and meteorological drivers. The ratio of the column density of atomic oxygen and molecular nitrogen (O/N\textsubscript{2}) is a useful parameter for quantifying this variability that has been shown to exhibit close correspondence to F-region electron density, total electron content and upper atmospheric transport. Therefore, understanding the variability in O/N\textsubscript{2} gives an insight into the geophysical variability of other relevant ionospheric and thermospheric parameters. The relative contributions of these drivers for thermospheric variability is not well known. Here we report a new analysis of the variability in O/N\textsubscript{2} to identify the sources of variability in a 55-day time period. Principal Component Analysis (PCA) was performed on thermospheric O/N\textsubscript{2} column density ratio from days 81 to 135 of 2020 from NASA's Global-scale Observations of the Limb and Disk (GOLD) mission. We find that geomagnetic activity is the major source of variability in O/N\textsubscript{2} column density ratio, followed by solar-driven transport and meteorological driving from the lower atmosphere. The first component (PC1) showed a strong correlation to Kp index and IMF, and geomagnetic storm effects are seen in the wavelet analysis of PC1's weights. The fifth component (PC5) showed a strong quasi-6-day oscillation(Q6DO). The higher explained variance ratio of PC1 suggests a stronger effect of geomagnetic activity relative to meteorological forcing from planetary scale waves. The methodology of the present study also demonstrates how PCA can be used to isolate and rank different sources of variability in other IT parameters.

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.