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A diffusive model of the turbulent mixing of dry and cloudy air
Author(s) -
Baker M. B.,
Latham J.
Publication year - 1982
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49710845809
Subject(s) - turbulence , mixing (physics) , drop (telecommunication) , liquid water content , dissipation , saturation (graph theory) , mechanics , dilution , atmospheric sciences , buoyancy , environmental science , meteorology , physics , thermodynamics , cloud computing , mathematics , telecommunications , quantum mechanics , combinatorics , computer science , operating system
Abstract A model is presented of the turbulent mixing between a shere of droplet‐free air (saturated or under‐saturated) and a spherical volume of cloud within which it is embedded. The rates of equalization of super‐saturation, temperature and liquid water are examined as functions of the turbulent energy dissipation rate, the dimensions of the interacting volumes, the drop‐size distribution in the cloud and other parameters. Spectral changes resulting from the mixing conform closely with those predicted by the recent inhomogeneous or dilution‐only descriptions of mixing (Baker et al. 1980; Telford and Chai 1980). It is shown that spectral changes observed during entainment into shallow cumulus, stratocumulus and cap clouds are good agreement with those predicted on the basis of this diffusive model. Calculations of mixing in the presence of an updraught yield size‐distributions (including bimodal spectra) similar to those oberved in natural clouds. Calculations of mixing during descent from cloud‐top suggest that regions of substantial under‐saturation may exist in the deep interiors of clouds which are entraining environmental air at their summits. Crude estimates of the degree of lateral spreading produced by turbulence as this descent proceeds indicates that significant horizontal structure in the water properties may exist throughout a substantial fraction of the cloud‐depth.