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The impact of the cooling time‐scale on the subgrid moisture field during cloud formation through homogeneous cooling
Author(s) -
Stiller Olaf
Publication year - 2003
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 - 10.1256/qj.02.199
Subject(s) - mixing (physics) , liquid water content , buoyancy , moisture , homogeneous , environmental science , meteorology , degrees of freedom (physics and chemistry) , energy budget , atmospheric sciences , cloud computing , cloud height , materials science , water content , mechanics , thermodynamics , cloud cover , physics , geology , computer science , geotechnical engineering , quantum mechanics , operating system
Cloud formation induced by homogeneous cooling has recently been found to substantially alter the moisture distribution. This study uses cloud‐resolving simulations of an idealized atmospheric layer to investigate the impact of the cooling time τ (i.e. of how fast the cooling is applied) on this process. The findings can be interpreted as an increased mixing (of air with different moisture content) for increasing τ. More specifically the mixing‐induced decrease of the moisture fluctuations and the corresponding decrease of the cloud water content are stronger for larger τ. This enhanced mixing is explained by the atmosphere's fast degrees of freedom (related to buoyancy oscillations) whose influence is found to grow for increasing τ. Exploiting scale separation between the different time‐scales, the behaviour of the fast degrees of freedom is deduced from the system's energy budget where the energy of the fast degrees of freedom is produced by the slow cooling process. © Crown copyright, 2003. Royal Meteorological Society