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Title: Cumulus convection
Author: Betts, Alan Keith
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 1970
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This thesis discusses the transports of sensible heat and water vapour by ordinary convection in a field of non-precipitating cumulus clouds. The stratification and time development of the convective boundary layer during dry and moist convection are investigated theoretically. A model is proposed which distinguishes for budget purposes 3 layers: the sub-cloud layer, and an upper and lower part of the cumulus layer. The model relates the cumulus convection to the surface boundary conditions, the 'free' atmosphere above the cumulus layer, and the large scale vertical motion. The significant aspects of the thesis are as follows: (1) Formulae for the dilution of clouds by their environment show the essential irreversibility of the vertical transports in non-precipitating cumulus convection. One significant consequence is that the convection destabilises the layer it occupies. (2) A new conservative variable, θL, related to potential temperature and liquid water mixing ratio, greatly simplifies the understanding of cloud parcel thermodynamics and cloud heat transports. With this variable dry and wet convection become closely analogous. (3) A mass transport model is used to clarify the mechanism of modification.of the mean atmosphere by the convection. (4) A model for the sub-cloud layer predicts from the surface fluxes and the large scale vertical motion the convective mass flux into the cumulus layer (a measure of the amount of active cloud). (5) A lapse-rate model is developed by relating the mechanics and thermodynamics of a typical cloud to the mean stratification, so as to predict the lapse rate characteristic of the cumulus layer. The control of cloud-base variations and large-scale vertical motion on cumulus convection is made quantitative. For example rise of cloud-base and large-scale subsidence are found to have some closely similar quantitative effects: both tend to suppress clouds.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available