Improving Representation of Tropical Cloud Overlap in GCMs Based on Cloud-Resolving Model Data |
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| Authors: | Xianwen Jing Hua Zhang Masaki Satoh Shuyun Zhao |
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| Institution: | 1.Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters,Nanjing University of Information Science & Technology,Nanjing,China;2.State Key Laboratory of Severe Weather,Chinese Academy of Meteorological Sciences,Beijing,China;3.Atmosphere and Ocean Research Institute,The University of Tokyo,Kashiwa,Japan;4.Laboratory for Climate Studies,National Climate Center, China Meteorological Administration,Beijing,China |
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| Abstract: | The decorrelation length (Lcf) has been widely used to describe the behavior of vertical overlap of clouds in general circulation models (GCMs); however, it has been a challenge to associate Lcf with the large-scale meteorological conditions during cloud evolution. This study explored the relationship between Lcf and the strength of atmospheric convection in the tropics based on output from a global cloud-resolving model. Lcf tends to increase with vertical velocity in the mid-troposphere (w500) at locations of ascent, but shows little or no dependency on w500 at locations of descent. A representation of Lcf as a function of vertical velocity is obtained, with a linear regression in ascending regions and a constant value in descending regions. This simple and dynamic-related representation of Lcf leads to a significant improvement in simulation of both cloud cover and radiation fields compared with traditional overlap treatments. This work presents a physically justifiable approach to depicting cloud overlap in the tropics in GCMs. |
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