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...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.展开更多
基金Supported by the National Key Research and Development Program of China(2017YFA0603502)(Key)National Natural Science Foundation of China(91644211 and 41375080)China Meteorological Administration Special Public Welfare Research Fund(GYHY201406023)
文摘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.
