Open AccessMicrophysical Scaling Relations in a Kinematic Model of Isolated Shallow Cumulus Clouds
Author(s) -
Axel Seifert,
Björn Stevens
Publication year - 2010
Publication title -
journal of the atmospheric sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.853
H-Index - 173
eISSN - 1520-0469
pISSN - 0022-4928
DOI - 10.1175/2009jas3319.1
Subject(s) - coalescence (physics) , scaling , cloud computing , precipitation , kinematics , environmental science , cloud physics , scale (ratio) , collision , statistical physics , meteorology , physics , atmospheric sciences , mechanics , classical mechanics , geometry , computer science , mathematics , astrobiology , operating system , computer security , quantum mechanics
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