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Scale‐aware parameterization of liquid cloud inhomogeneity and its impact on simulated climate in CESM
Author(s) -
Xie Xin,
Zhang Minghua
Publication year - 2015
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2015jd023565
Subject(s) - latitude , cloud computing , longitude , atmosphere (unit) , environmental science , grid , liquid water path , atmospheric model , atmospheric sciences , water vapor , scale (ratio) , meteorology , shape parameter , computational physics , physics , geology , computer science , mathematics , geodesy , precipitation , statistics , quantum mechanics , astronomy , operating system
Using long‐term radar‐based ground measurements from the Atmospheric Radiation Measurement Program, we derive the inhomogeneity of cloud liquid water as represented by the shape parameter of a gamma distribution. The relationship between the inhomogeneity and the model grid size as well as atmospheric condition is presented. A larger grid scale and more unstable atmosphere are associated with larger inhomogeneity that is described by a smaller shape parameter. This relationship is implemented as a scale‐aware parameterization of the liquid cloud inhomogeneity in the Community Earth System Model (CESM) in which the shape parameter impacts the cloud microphysical processes. When used in the default CESM1 with the finite‐volume dynamic core where a constant liquid inhomogeneity parameter was assumed, it reduces the cloud inhomogeneity in high latitudes and increases it in low latitudes. This is due to both the smaller (larger) grid size in high (low) latitudes in the longitude‐latitude grid setting of CESM and the more stable (unstable) atmosphere. The single‐column model and general circulation model sensitivity experiments show that the new parameterization increases the cloud liquid water path in polar regions and decreases it in low latitudes. An advantage of the parameterization is that it can recognize the spatial resolutions of the CESM without special tuning of the cloud water inhomogeneity parameter.