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Title: Simple models of the mean meridional circulation
Author: Edgington, B. P.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1996
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It is a characteristic of the middle atmosphere that, for the most part, it is strongly stably stratified and rapidly rotating. These two conditions respectively act to inhibit the vertical and latitudinal motion of air. A consequence of this is that the middle atmosphere is particularly amenable to simplifications in terms both of describing it, and of modelling it. It can be treated to a first approximation as axisymmetric, since middle atmospheric conditions often vary much more with latitude and height than with longitude. Although air mass motion in the meridional plane is inhibited in the middle atmosphere, there is good evidence of a persistent mean meridional circulation (MMC) on seasonal timescales. This meridional circulation provides a means by which anthropogenic gases can enter the stratosphere, be carried out to the mesosphere and descend over the poles. Thus, it is of great importance from the viewpoint of photo-chemistry, and the ozone hole. The first part of this dissertation is concerned with the middle atmosphere as simplified by taking the zonal means of the relevant quantities, that is, making it axisymmetric. The climatology of the zonal-mean observed atmosphere is discussed. The main discussion is concerned with the generation of a MMC in such model atmospheres. First an analytic model is discussed, after Eliassen (1951), showing the importance of zonal-mean heating and zonal-mean mechanical forcing in the generation of the MMC. The origin of these forcings in terms of wave-mean interaction is discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available