Gravity waves play a crucial role in the dynamics of the middle atmosphere through the vertical transport of tropospheric energy and momentum. Despite the importance of gravity wave effects, nearly all general circulation models significantly underestimate gravity wave drag around the southern wintertime polar vortex, leading to large discrepancies from observed behaviour and a strong impediment to model progress. Here we use GPS radio occultation data from the COSMIC satellite constellation to investigate key properties of gravity waves in and around the southern polar vortex and over the gravity wave hot spot of the southern Andes/Drake Passage/Antarctic Peninsula. We also develop spectral analysis tools in order to further the capabilities of our data for this purpose.By analysing vertical profiles of atmospheric temperature from COSMIC, we find evidence of the meridional propagation of waves into the polar vortex from sources far to the north. We develop a new wavelet-based analysis technique for the quantitative identification of gravity waves in COSMIC profiles, and use it to investigate gravity wave intermittency over the hot spot region and around the edge of the polar vortex. We then estimate gravity wave momentum flux over the hot spot from closely-spaced pairs of COSMIC profiles.Finally, we develop a new two-dimensional spectral analysis method for the measurement of gravity wave amplitudes, horizontal wavelengths and directions of propagation from AIRS measurements, based upon the two-dimensional Stockwell transform. We show that, by using an alternative elliptical spectral window, we can dramatically improve the measurement of wave amplitude. We apply our two-dimensional Stockwell transform to AIRS measurements over the known gravity wave hot spots of South Georgia and the Antarctic Peninsula, measuring gravity properties and momentum fluxes with improved confidence, accuracy and rigour over current methods.
|Date of Award||7 Jun 2016|
|Supervisor||Nicholas Mitchell (Supervisor)|