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Title: Stratosphere-troposphere dynamical coupling
Author: Hardiman, S. C.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2007
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This thesis is concerned with dynamical coupling between the stratosphere and troposphere. The first part of the thesis examines mechanisms whereby dynamical perturbations to the upper stratosphere can lead to a significant response in the lower stratosphere, looking particularly at how this response is determined by the extra-tropical dynamics. A one dimensional model is used to show that the response is much greater when the external parameters are such that the flow has multiple stable states. The same principle is shown to apply to a fully three dimensional flow and does not depend qualitatively on the representation of the troposphere and tropospheric wave forcing. The dependence of the response on the height of the applied dynamical perturbation, the amplitude of planetary wave forcing, and the relaxation to radiative equilibrium temperatures is considered. In the second part of the thesis we consider the interhemispheric differences in the extratropical seasonal cycle and suggest that resonance of topographically forced waves with free travelling planetary waves could be in part responsible for these differences. The seasonal cycle in mass upwelling in the tropical lower stratosphere is also considered. In particular we look at the differences in this upwelling caused by the strength and location of tropospheric wave driving, the thermal relaxation timescale of the atmosphere, baroclinic instability, and the seasonal cycle in the tropospheric radiative equilibrium temperature field. Finally we consider the interannual variability seen in the tropical mass upwelling. We quantify the different parts of this variability – the part that can be considered forced variability and the part that arises due to internal variability. We suggest that the high forced variability seen in the mass upwelling may be due to it being linked, via extratropical wave driving, to sea surface temperatures.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available