On the Variation of Column $O/N\textsubscript{2} $ in
the upper atmosphere using Principal Component Analysis in 2-dimensional
images
Abstract
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.