Characteristics of cloud overlap over Eastern Asia are analyzed using a threeyear dataset （20072009） from the cloud observing satellite CloudSat. Decorrelation depth Lis retrieved, which represents cloud overlap cha...Characteristics of cloud overlap over Eastern Asia are analyzed using a threeyear dataset （20072009） from the cloud observing satellite CloudSat. Decorrelation depth Lis retrieved, which represents cloud overlap characteristics in the simulation of cloudradiation processes in global climate models. Results show that values of L in six study regions are generally within the range 03 km. By categorizing L according to cloud amount in subregions, peak L appears near subregions with cloud amount between 0.6 and 0.8. Average L is 2.5 km. L at higher altitudes is generally larger than at lower lati tudes. Seasonal variations of L are also clearly demonstrated. The sensitivity of cloud radiative forcing （CRF） to L;y in Community Atmosphere Model 3.0 of the National Center for Atmospheric Research （CAM3/NCAR） is analyzed. The result shows that L can have a big impact on simulation of CRF, especially in major monsoon regions and the MidEastern Pacif ic, where the difference in CRF can reach 4050 W m2. Therefore, accurate parameterization of cloud vertical overlap struc ture is important to CRF simulation and its feedback to climate.展开更多
The latest advances in studies on the treatment of cloud overlap and its radiative transfer in global climate models are summarized.Developments with respect to this internationally challenging problem are described f...The latest advances in studies on the treatment of cloud overlap and its radiative transfer in global climate models are summarized.Developments with respect to this internationally challenging problem are described from aspects such as the design of cloud overlap assumptions,the realization of cloud overlap assumptions within climate models,and the data and methods used to obtain consistent observations of cloud overlap structure and radiative transfer in overlapping clouds.To date,there has been an appreciable level of achievement in studies on cloud overlap in climate models,demonstrated by the development of scientific assumptions（e.g.,e-folding overlap） to describe cloud overlap,the invention and broad application of the fast radiative transfer method for overlapped clouds（Monte Carlo Independent Column Approximation）,and the emergence of continuous 3D cloud satellite observation（e.g.,CloudSat/CALIPSO） and cloud-resolving models,which provide numerous data valuable for the exact description of cloud overlap structure in climate models.However,present treatments of cloud overlap and its radiative transfer process are far from complete,and there remain many unsettled problems that need to be explored in the future.展开更多
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
The improvement of the accuracy of simulated cloud-related variables,such as the cloud fraction,in global climate models(GCMs)is still a challenging problem in climate modeling.In this study,the influence of cloud mic...The improvement of the accuracy of simulated cloud-related variables,such as the cloud fraction,in global climate models(GCMs)is still a challenging problem in climate modeling.In this study,the influence of cloud microphysics schemes(one-moment versus two-moment schemes)and cloud overlap methods(observation-based versus a fixed vertical decorrelation length)on the simulated cloud fraction was assessed in the BCC_AGCM2.0_CUACE/Aero.Compared with the fixed decorrelation length method,the observation-based approach produced a significantly improved cloud fraction both globally and for four representative regions.The utilization of a two-moment cloud microphysics scheme,on the other hand,notably improved the simulated cloud fraction compared with the one-moment scheme;specifically,the relative bias in the global mean total cloud fraction decreased by 42.9%–84.8%.Furthermore,the total cloud fraction bias decreased by 6.6%in the boreal winter(DJF)and 1.64%in the boreal summer(JJA).Cloud radiative forcing globally and in the four regions improved by 0.3%−1.2% and 0.2%−2.0%,respectively.Thus,our results showed that the interaction between clouds and climate through microphysical and radiation processes is a key contributor to simulation uncertainty.展开更多
基金supported by National Basic Research Program of China (Grant No. 2011CB403405)National Natural Science Foundation of China (Grant No. 41075056)Public Meteorology Special Foundation of MOST (Grant No. GYHY201106022)
文摘Characteristics of cloud overlap over Eastern Asia are analyzed using a threeyear dataset （20072009） from the cloud observing satellite CloudSat. Decorrelation depth Lis retrieved, which represents cloud overlap characteristics in the simulation of cloudradiation processes in global climate models. Results show that values of L in six study regions are generally within the range 03 km. By categorizing L according to cloud amount in subregions, peak L appears near subregions with cloud amount between 0.6 and 0.8. Average L is 2.5 km. L at higher altitudes is generally larger than at lower lati tudes. Seasonal variations of L are also clearly demonstrated. The sensitivity of cloud radiative forcing （CRF） to L;y in Community Atmosphere Model 3.0 of the National Center for Atmospheric Research （CAM3/NCAR） is analyzed. The result shows that L can have a big impact on simulation of CRF, especially in major monsoon regions and the MidEastern Pacif ic, where the difference in CRF can reach 4050 W m2. Therefore, accurate parameterization of cloud vertical overlap struc ture is important to CRF simulation and its feedback to climate.
基金Supported by the China Meteorological Administration Special Public Welfare Research Fund(GYHY201406023)National Natural Science Foundation of China(41375080)
文摘The latest advances in studies on the treatment of cloud overlap and its radiative transfer in global climate models are summarized.Developments with respect to this internationally challenging problem are described from aspects such as the design of cloud overlap assumptions,the realization of cloud overlap assumptions within climate models,and the data and methods used to obtain consistent observations of cloud overlap structure and radiative transfer in overlapping clouds.To date,there has been an appreciable level of achievement in studies on cloud overlap in climate models,demonstrated by the development of scientific assumptions（e.g.,e-folding overlap） to describe cloud overlap,the invention and broad application of the fast radiative transfer method for overlapped clouds（Monte Carlo Independent Column Approximation）,and the emergence of continuous 3D cloud satellite observation（e.g.,CloudSat/CALIPSO） and cloud-resolving models,which provide numerous data valuable for the exact description of cloud overlap structure in climate models.However,present treatments of cloud overlap and its radiative transfer process are far from complete,and there remain many unsettled problems that need to be explored in the future.
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.
基金supported by the National Key R&D Program of China(2017YFA0603502)(Key)National Natural Science Foundation of China(91644211)S&T Development Fund of CAMS(2021KJ004).
文摘The improvement of the accuracy of simulated cloud-related variables,such as the cloud fraction,in global climate models(GCMs)is still a challenging problem in climate modeling.In this study,the influence of cloud microphysics schemes(one-moment versus two-moment schemes)and cloud overlap methods(observation-based versus a fixed vertical decorrelation length)on the simulated cloud fraction was assessed in the BCC_AGCM2.0_CUACE/Aero.Compared with the fixed decorrelation length method,the observation-based approach produced a significantly improved cloud fraction both globally and for four representative regions.The utilization of a two-moment cloud microphysics scheme,on the other hand,notably improved the simulated cloud fraction compared with the one-moment scheme;specifically,the relative bias in the global mean total cloud fraction decreased by 42.9%–84.8%.Furthermore,the total cloud fraction bias decreased by 6.6%in the boreal winter(DJF)and 1.64%in the boreal summer(JJA).Cloud radiative forcing globally and in the four regions improved by 0.3%−1.2% and 0.2%−2.0%,respectively.Thus,our results showed that the interaction between clouds and climate through microphysical and radiation processes is a key contributor to simulation uncertainty.
