A Survey of Seasonal, Hemispheric and Interannual Variations in the Gravity Wave Spectrum in the Upper Stratosphere and Lower Mesosphere

Abstract

This thesis presents for the first time a comprehensive, multi-year analysis of gravity waves (GWs) in the Earth's middle atmosphere using satellite observations from the Cloud Imaging and Particle Size (CIPS) instrument and the Atmospheric Infrared Sounder (AIRS). Data from the years 2019–2021 are examined, covering both stratospheric and mesospheric altitudes and focusing on four representative months: January, February, July, and August. CIPS and AIRS datasets are processed using custom-built spectral analysis pipelines to extract horizontal wavelengths, amplitudes, and propagation direction information, with specific emphasis on the overlapping observational region between ±60° latitude. We assess the spatial, seasonal, and interannual variability of GW characteristics, comparing zonal and meridional wavelength distributions across hemispheres and investigating the effects of dynamical events such as sudden stratospheric warmings (SSWs). Results reveal that CIPS captures significant seasonal shifts and hemispheric asymmetries in GW activity—particularly during winter months with active SSW events—while AIRS exhibits more stable directional distributions with dominant longer horizontal wavelengths. By separating zonal and meridional components and conducting regional 1D and 2D analyses, we demonstrate that combining mesospheric and stratospheric observations provides new insights into the vertical coupling and geographic variability of atmospheric wave dynamics. This study emphasizes the importance of multi-platform GW analysis in advancing our understanding of atmospheric circulation and climate variability.