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Fluctuations in an Equilibrium Convective Ensemble. Part II: Numerical Experiments

Cohen, Brenda G. and Craig, George C. (2006) Fluctuations in an Equilibrium Convective Ensemble. Part II: Numerical Experiments. Journal of the Atmospheric Sciences, 63, pp. 2005-2015. DOI: 10.1175/JAS3709.1.

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The theoretical predictions derived in Part I of this study for the equilibrium fluctuations of an idealized ensemble of noninteracting, pointlike cumulus clouds are tested against three-dimensional cloud resolving model (CRM) simulations of radiative–convective equilibrium. Simulations with different radiative cooling rates are used to give a range of cloud densities, while imposed vertical wind shear of different strengths is used to produce different degrees of convective organization. The distribution of mass flux of individual clouds is found to be exponential in all simulations, in agreement with the theory. The distribution of total mass flux over a finite region also agrees well (to within around 10%) with the theoretical prediction for all simulations, but only after a correction to the modeled variance to take account of the finite size of clouds has been made. In the absence of imposed vertical wind shear, some spatial clustering of convective cells is observed at lower forcings (−2 and −4 K day−1) on a scale of 10–20 km, while at higher forcings (−8, −12, and −16 K day−1), there is a tendency toward spatial regularity on the same scale. These localized cloud interactions, however, appear to have little effect on the magnitude of the mass flux variability. Surprisingly, the convective organization obtained in the simulations with vertical wind shear has only a small effect on the mass flux statistics, even though it shows clearly in the location of the clouds.

Document Type:Article
Title:Fluctuations in an Equilibrium Convective Ensemble. Part II: Numerical Experiments
AuthorsInstitution or Email of Authors
Cohen, Brenda G.Univ. of Reading, Reading, UK
Journal or Publication Title:Journal of the Atmospheric Sciences
Refereed publication:Yes
In ISI Web of Science:Yes
Page Range:pp. 2005-2015
Keywords:convective ensemble, equilibrium fluctuations, cloud resolving model
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Space (old)
HGF - Program Themes:W EO - Erdbeobachtung
DLR - Research area:Space
DLR - Program:W EO - Erdbeobachtung
DLR - Research theme (Project):W - Vorhaben Atmosphären- und Klimaforschung (old)
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Cloud Physics and Traffic Meteorology
Deposited By: Jana Freund
Deposited On:24 Jul 2007
Last Modified:11 Nov 2014 21:56

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