Divyam Goel

and 6 more

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.

Federico Gasperini

and 3 more

It is now well established that waves generated in the lower atmosphere can propagate upward and significantly impact the dynamics and mean state of the ionosphere-thermosphere (IT, 100-600 km) system. Given the geometry of magnetic field lines near the equator, a significant fraction of this IT coupling occurs at low latitudes and is driven by global-scale waves of tropical tropospheric origin, such as the diurnal eastward-propagating tide with zonal wavenumber 3 (DE3) and the ultra-fast Kelvin wave (UFKW). Despite recent progress, lack of coincident global observations has thus far precluded full characterization of the sources of day-today variability of these waves, including nonlinear interactions, and impacts on the low-latitude IT. In this work, in-situ ion densities from Ionospheric Connection Explorer (ICON) and Constellation Observing System for Meteorology, Ionosphere and Climate 2 (COSMIC-2) Ion Velocity Meter (IVM) along with remotely-sensed zonal winds from ICON Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) are used to reveal a rich spectrum of waves coupling the lower (∼90-105 km) and middle (∼200-270 km) thermosphere with the upper F-region (∼540 and ∼590 km) ionosphere. Spectral analyses for a 40-day period of similar local time demonstrate prominent IT coupling via DE3, a 3-day UFKW, and the two ∼1.43-day and ∼0.77-day secondary waves from their nonlinear interactions. While all these waves are found to dominate the F-region spectra, only the UFKW and the 1.43-day secondary wave can propagate to ∼270 km suggesting E-region wind dynamo processes as major contributors to their observed ionospheric signatures.