This thesis presents the results from investigations into various features of the dynamics of the middle atmosphere.Wind measurements from the meteor radar on Ascension Island and temperatures measured by the Aura MLS instrument are used to characterise Ultra-Fast Kelvin Waves (UFKW) in the MLT-region. Rainfall rates from TRMM are used as a proxy for latent heat release in an investigation of the excitation of UFKW, and results are compared with predictions of the Kyushu-GCM. Amplitudes and vertical wavelengths are determined, as are the accelerations resulting from wave dissipation. Intra-seasonal oscillations (ISOs) are observed in the wave amplitudes and accelerations, and oscillations with the same periods are observed in the rainfall and MLT-region winds, suggesting that UFKW play a role in carrying the tropospheric ISOs to higher regions.The seasonal and interannual variability of the tidal field over Ascension Island is investigated. Amplitudes, phases and vertical wavelengths of the diurnal and semidiurnal tides are reported on. Our observations of tidal parameters are compared with the predictions of the extended Canadian Middle Atmosphere Model (eCMAM) and the Whole Atmosphere Community Climate Model (WACCM). Correlations between tidal amplitudes, the stratospheric Quasi-Biennial Oscillation (QBO) and the El Nin ̃o Southern Oscillation (ENSO) are discussed.The Hocking (2005) method is adapted to recover monthly-mean gravity-wave momentum fluxes and wind variances either side of the Drake passage gravity-wave hotspot. The ability of the method to recover momentum fluxes over each radar are tested by sampling a series of specified (known) wave fields of increasing complexity with the actual meteor distributions, and comparing the recovered momentum fluxes with the specified values. The analysis is then applied to the real data to obtain climatologies of the MLT-region variances and momentum fluxes for a composite year of the 2008 to 2012 data.
|Date of Award
|19 Aug 2014
|Nicholas Mitchell (Supervisor)
- Middle atmosphere dynamics
- Meteor radar