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Moist halo regions around shallow cumulus clouds in large eddy simulations

Gu, J.-F. ORCID:, Plant, B. ORCID:, Holloway, C. ORCID: and Clark, P. ORCID: (2023) Moist halo regions around shallow cumulus clouds in large eddy simulations. Quarterly Journal of the Royal Meteorological Society. ISSN 1477-870X (In Press)

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In this study, the moist buffering halo region of shallow maritime cumulus clouds is systematically investigated using large eddy simulations with various grid resolutions and numerical choices. Auto-correlation analyses of cloud liquid water and relative humidity suggest a converged size of 200 − 300 m for moist patches outside clouds when model resolution is below 50 m but may overestimate this size due to non-cloudy moist regions. Based on a composite analysis, the structure of the moist halo immediately outside individual clouds is examined. It is found that, regardless of model resolution, the distribution of relative humidity in the halo region does not depend on cloud size, but on the real distance away from the cloud boundary, indicating some size-independent length scales responsible for the halo formation. The relative humidity decays with distance more quickly with finer horizontal resolution, which is possibly related to the model resolution dependency of the cloud spectrum. The halo size near cloud base is larger than that within the cloud layer and this feature is robust across all simulations. Further analyses of backward and forward Lagrangian trajectories originating from the moist halo region reveal the possible role for sub-cloud coherent structures on the cloud-base halo formation. Possible mechanisms explaining cloud halo sizes and associated length scales are discussed.

Item Type:Article
Divisions:Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
ID Code:114225
Uncontrolled Keywords:shallow cumulus clouds, moist halo region, length scales, large eddy simulations
Publisher:Royal Meteorological Society

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