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Journal Article

Microphysical scaling relations in a kinematic model of isolated shallow cumulus clouds

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Stevens,  Bjorn       
Director’s Research Group AES, The Atmosphere in the Earth System, MPI for Meteorology, Max Planck Society;

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Citation

Seifert, A., & Stevens, B. (2010). Microphysical scaling relations in a kinematic model of isolated shallow cumulus clouds. Journal of the Atmospheric Sciences, 67, 1575-1590. doi:10.1175/2009JAS3319.1.


Cite as: https://hdl.handle.net/11858/00-001M-0000-0011-F5FF-4
Abstract
The rain formation in shallow cumulus clouds by condensational growth and collision-coalescence of liquid drops is revisited with the aim of understanding the controls on precipitation efficiency for idealized cloud drafts. For the purposes of this analysis, a one-dimensional kinematic cloud model is introduced, which permits the efficient exploration of many microphysical aspects of liquid shallow clouds with both spectral and two-moment bulk microphysical formulations. Based on the one-dimensional model and the insights gained from both microphysical approaches, scaling relations are derived that provide a link between microphysical and macroscopic cloud properties. By introducing the concept of a macroscopic autoconversion time scale, the rain formation can be traced back to quantities such as cloud depth, average vertical velocity, lapse rate, and cloud lifetime. The one-dimensional model also suggests that the precipitation efficiency can be expressed as a function of the ratio of the macroscopic autoconversion time scale and cloud lifetime and that it exhibits threshold-like behavior.