scholarly journals A new two-moment bulk stratiform cloud microphysics scheme in the Community Atmosphere Model (CAM3), Part I: Description and numerical tests

2007 ◽  
Vol preprint (2008) ◽  
pp. 1
Author(s):  
Hugh Morrison ◽  
Andrew Gettelman
Keyword(s):  
Cloud Microphysics ◽  
Stratiform Cloud ◽  
Microphysics Scheme ◽  
Numerical Tests ◽  
Community Atmosphere Model ◽  
Atmosphere Model

scholarly journals A sensitivity study of radiative fluxes at the top of atmosphere to cloud-microphysics and aerosol parameters in the community atmosphere model CAM5

2013 ◽  
Vol 13 (21) ◽  
pp. 10969-10987 ◽  
Author(s):  
C. Zhao ◽  
X. Liu ◽  
Y. Qian ◽  
J. Yoon ◽  
Z. Hou ◽  
...  
Keyword(s):  
Regional Scale ◽  
Cloud Microphysics ◽  
Model Parameters ◽  
Parameter Uncertainties ◽  
Dimensional Parameter ◽  
Individual Parameter ◽  
Radiative Fluxes ◽  
Community Atmosphere Model ◽  
Atmosphere Model ◽  
Global Mean

Abstract. In this study, we investigated the sensitivity of net radiative fluxes (FNET) at the top of atmosphere (TOA) to 16 selected uncertain parameters mainly related to the cloud microphysics and aerosol schemes in the Community Atmosphere Model version 5 (CAM5). We adopted a quasi-Monte Carlo (QMC) sampling approach to effectively explore the high-dimensional parameter space. The output response variables (e.g., FNET) are simulated using CAM5 for each parameter set, and then evaluated using the generalized linear model analysis. In response to the perturbations of these 16 parameters, the CAM5-simulated global annual mean FNET ranges from −9.8 to 3.5 W m−2 compared to 1.9 W m−2 with the default parameter values. Variance-based sensitivity analysis is conducted to show the relative contributions of individual parameter perturbations to the global FNET variance. The results indicate that the changes in the global mean FNET are dominated by changes in net cloud forcing (CF) within the parameter ranges being investigated. The threshold size parameter related to auto-conversion of cloud ice to snow is identified as one of the most influential parameters for FNET in CAM5 simulations. The strong heterogeneous geographic distribution of FNET variance shows that parameters have a clear localized effect over regions where they are acting. However, some parameters also have non-local impacts on FNET variance. Although external factors, such as perturbations of anthropogenic and natural emissions, largely affect FNET variance at the regional scale, their impact is weaker than that of model internal parameters in terms of simulating global mean FNET. The interactions among the 16 selected parameters contribute a relatively small portion to the total FNET variance over most regions of the globe. This study helps us better understand the parameter uncertainties in the CAM5 model, and thus provides information for further calibrating uncertain model parameters with the largest sensitivity.

scholarly journals A sensitivity study of radiative fluxes at the top of atmosphere to cloud-microphysics and aerosol parameters in the Community Atmosphere Model CAM5

2013 ◽  
Vol 13 (5) ◽  
pp. 12135-12176 ◽  
Author(s):  
C. Zhao ◽  
X. Liu ◽  
Y. Qian ◽  
J. Yoon ◽  
Z. Hou ◽  
...  
Keyword(s):  
Regional Scale ◽  
Cloud Microphysics ◽  
Model Parameters ◽  
Parameter Uncertainties ◽  
Dimensional Parameter ◽  
Individual Parameter ◽  
Radiative Fluxes ◽  
Community Atmosphere Model ◽  
Atmosphere Model ◽  
Global Mean

Abstract. In this study, we investigated the sensitivity of net radiative fluxes (FNET) at the top of atmosphere (TOA) to 16 selected uncertain parameters mainly related to the cloud microphysics and aerosol schemes in the Community Atmosphere Model version 5 (CAM5). We adopted a quasi-Monte Carlo (QMC) sampling approach to effectively explore the high dimensional parameter space. The output response variables (e.g., FNET) were simulated using CAM5 for each parameter set, and then evaluated using the generalized linear model analysis. In response to the perturbations of these 16 parameters, the CAM5-simulated global annual mean FNET ranges from −9.8 to 3.5 W m−2 compared to the CAM5-simulated FNET of 1.9 W m−2 with the default parameter values. Variance-based sensitivity analysis was conducted to show the relative contributions of individual parameter perturbation to the global FNET variance. The results indicate that the changes in the global mean FNET are dominated by those of net cloud forcing (CF) within the parameter ranges being investigated. The threshold size parameter related to auto-conversion of cloud ice to snow is identified as one of the most influential parameters for FNET in CAM5 simulations. The strong heterogeneous geographic distribution of FNET variance shows parameters have a clear localized effect over regions where they are acting. However, some parameters also have non-local impacts on FNET variance. Although external factors, such as perturbations of anthropogenic and natural emissions, largely affect FNET variance at the regional scale, their impact is weaker than that of model internal parameters in terms of simulating global mean FNET. The interactions among the 16 selected parameters contribute a relatively small portion to the total FNET variance over most regions of the globe. This study helps us better understand the parameter uncertainties in the CAM5 model, and thus provides information for further calibrating uncertain model parameters with the largest sensitivity.

scholarly journals Evaluation of Microphysics Parameterization for Convective Clouds in the NCAR Community Atmosphere Model CAM5

2012 ◽  
Vol 25 (24) ◽  
pp. 8568-8590 ◽  
Author(s):  
Xiaoliang Song ◽  
Guang J. Zhang ◽  
J.-L. F. Li
Keyword(s):  
Large Scale ◽  
Convective Cloud ◽  
Number Concentration ◽  
Liquid Water Path ◽  
Microphysics Scheme ◽  
Convective Clouds ◽  
Community Atmosphere Model ◽  
Atmosphere Model ◽  
Subtropical Oceans ◽  
The Impact

Abstract A physically based two-moment microphysics parameterization scheme for convective clouds is implemented in the NCAR Community Atmosphere Model version 5 (CAM5) to improve the representation of convective clouds and their interaction with large-scale clouds and aerosols. The explicit treatment of mass mixing ratio and number concentration of cloud and precipitation particles enables the scheme to account for the impact of aerosols on convection. The scheme is linked to aerosols through cloud droplet activation and ice nucleation processes and to stratiform cloud parameterization through convective detrainment of cloud liquid/ice water content (LWC/IWC) and droplet/crystal number concentration (DNC/CNC). A 5-yr simulation with the new convective microphysics scheme shows that both cloud LWC/IWC and DNC/CNC are in good agreement with observations, indicating the scheme describes microphysical processes in convection well. Moreover, the microphysics scheme is able to represent the aerosol effects on convective clouds such as the suppression of warm rain formation and enhancement of freezing when aerosol loading is increased. With more realistic simulations of convective cloud microphysical properties and their detrainment, the mid- and low-level cloud fraction is increased significantly over the ITCZ–southern Pacific convergence zone (SPCZ) and subtropical oceans, making it much closer to the observations. Correspondingly, the serious negative bias in cloud liquid water path over subtropical oceans observed in the standard CAM5 is reduced markedly. The large-scale precipitation is increased and precipitation distribution is improved as well. The long-standing precipitation bias in the western Pacific is significantly alleviated because of microphysics–thermodynamics feedbacks.

scholarly journals A unified parameterization of clouds and turbulence using CLUBB and subcolumns in the Community Atmosphere Model

2015 ◽  
Vol 8 (6) ◽  
pp. 5041-5088 ◽  
Author(s):  
K. Thayer-Calder ◽  
A. Gettelman ◽  
C. Craig ◽  
S. Goldhaber ◽  
P. A. Bogenschutz ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Climate Models ◽  
Convective Cloud ◽  
Global Climate Models ◽  
Liquid Water Path ◽  
Microphysics Scheme ◽  
Cloud Forcing ◽  
Community Atmosphere Model ◽  
Atmosphere Model ◽  
Cloud Parameterization

Abstract. Most global climate models parameterize separate cloud types using separate parameterizations. This approach has several disadvantages, including obscure interactions between parameterizations and inaccurate triggering of cumulus parameterizations. Alternatively, a unified cloud parameterization uses one equation set to represent all cloud types. Such cloud types include stratiform liquid and ice cloud, shallow convective cloud, and deep convective cloud. Vital to the success of a unified parameterization is a general interface between clouds and microphysics. One such interface involves drawing Monte Carlo samples of subgrid variability of temperature, water vapor, cloud liquid, and cloud ice, and feeding the sample points into a microphysics scheme. This study evaluates a unified cloud parameterization and a Monte Carlo microphysics interface that has been implemented in the Community Atmosphere Model (CAM) version 5.3. Results describing the mean climate and tropical variability from global simulations are presented. The new model shows a degradation in precipitation skill but improvements in short-wave cloud forcing, liquid water path, long-wave cloud forcing, precipitable water, and tropical wave simulation. Also presented are estimations of computational expense and investigation of sensitivity to number of subcolumns.

A New Two-Moment Bulk Stratiform Cloud Microphysics Scheme in the Community Atmosphere Model, Version 3 (CAM3). Part II: Single-Column and Global Results

2008 ◽  
Vol 21 (15) ◽  
pp. 3660-3679 ◽  
Author(s):  
A. Gettelman ◽  
H. Morrison ◽  
S. J. Ghan
Keyword(s):  
General Circulation ◽  
Circulation Model ◽  
Cloud Microphysics ◽  
Number Concentration ◽  
Radiation Budget ◽  
Cloud Particle ◽  
Microphysics Scheme ◽  
Community Atmosphere Model ◽  
Single Column ◽  
Rain Drops

Abstract The global performance of a new two-moment cloud microphysics scheme for a general circulation model (GCM) is presented and evaluated relative to observations. The scheme produces reasonable representations of cloud particle size and number concentration when compared to observations, and it represents expected and observed spatial variations in cloud microphysical quantities. The scheme has smaller particles and higher number concentrations over land than the standard bulk microphysics in the GCM and is able to balance the top-of-atmosphere radiation budget with 60% the liquid water of the standard scheme, in better agreement with retrieved values. The new scheme diagnostically treats both the mixing ratio and number concentration of rain and snow, and it is therefore able to differentiate the two key regimes, consisting of drizzle in shallow, warm clouds and larger rain drops in deeper cloud systems. The modeled rain and snow size distributions are consistent with observations.

scholarly journals A unified parameterization of clouds and turbulence using CLUBB and subcolumns in the Community Atmosphere Model

2015 ◽  
Vol 8 (12) ◽  
pp. 3801-3821 ◽  
Author(s):  
K. Thayer-Calder ◽  
A. Gettelman ◽  
C. Craig ◽  
S. Goldhaber ◽  
P. A. Bogenschutz ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Climate Models ◽  
Convective Cloud ◽  
Global Climate Models ◽  
Liquid Water Path ◽  
Microphysics Scheme ◽  
Cloud Forcing ◽  
Community Atmosphere Model ◽  
Atmosphere Model ◽  
Cloud Parameterization

Abstract. Most global climate models parameterize separate cloud types using separate parameterizations. This approach has several disadvantages, including obscure interactions between parameterizations and inaccurate triggering of cumulus parameterizations. Alternatively, a unified cloud parameterization uses one equation set to represent all cloud types. Such cloud types include stratiform liquid and ice cloud, shallow convective cloud, and deep convective cloud. Vital to the success of a unified parameterization is a general interface between clouds and microphysics. One such interface involves drawing Monte Carlo samples of subgrid variability of temperature, water vapor, cloud liquid, and cloud ice, and feeding the sample points into a microphysics scheme. This study evaluates a unified cloud parameterization and a Monte Carlo microphysics interface that has been implemented in the Community Atmosphere Model (CAM) version 5.3. Model computational expense is estimated, and sensitivity to the number of subcolumns is investigated. Results describing the mean climate and tropical variability from global simulations are presented. The new model shows a degradation in precipitation skill but improvements in shortwave cloud forcing, liquid water path, long-wave cloud forcing, precipitable water, and tropical wave simulation.

A New Two-Moment Bulk Stratiform Cloud Microphysics Scheme in the Community Atmosphere Model, Version 3 (CAM3). Part I: Description and Numerical Tests

2008 ◽  
Vol 21 (15) ◽  
pp. 3642-3659 ◽  
Author(s):  
Hugh Morrison ◽  
Andrew Gettelman
Keyword(s):  
General Circulation ◽  
Circulation Model ◽  
General Circulation Models ◽  
Cloud Microphysics ◽  
Small Time ◽  
Vertical Resolution ◽  
Time Step ◽  
Stratiform Cloud ◽  
Microphysics Scheme ◽  
Microphysical Processes

Abstract A new two-moment stratiform cloud microphysics scheme in a general circulation model is described. Prognostic variables include cloud droplet and cloud ice mass mixing ratios and number concentrations. The scheme treats several microphysical processes, including hydrometeor collection, condensation/evaporation, freezing, melting, and sedimentation. The activation of droplets on aerosol is physically based and coupled to a subgrid vertical velocity. Unique aspects of the scheme, relative to existing two-moment schemes developed for general circulation models, are the diagnostic treatment of rain and snow number concentration and mixing ratio and the explicit treatment of subgrid cloud water variability for calculation of the microphysical process rates. Numerical aspects of the scheme are described in detail using idealized one-dimensional offline tests of the microphysics. Sensitivity of the scheme to time step, vertical resolution, and numerical method for diagnostic precipitation is investigated over a range of conditions. It is found that, in general, two substeps are required for numerical stability and reasonably small time truncation errors using a time step of 20 min; however, substepping is only required for the precipitation microphysical processes rather than the entire scheme. A new numerical approach for the diagnostic rain and snow produces reasonable results compared to a benchmark simulation, especially at low vertical resolution. Part II of this study details results of the scheme in single-column and global simulations, including comparison with observations.

scholarly journals Impact of Environmental Aerosols on a Developing Extratropical Cyclone in the Superparameterized Community Atmosphere Model

2016 ◽  
Vol 29 (15) ◽  
pp. 5533-5546 ◽  
Author(s):  
Yi Lu ◽  
Yi Deng
Keyword(s):  
Growth Rate ◽  
Cold Front ◽  
Deep Convection ◽  
Regional Climate ◽  
Extratropical Cyclone ◽  
Latent Heating ◽  
Stratiform Cloud ◽  
Community Atmosphere Model ◽  
Moisture Supply ◽  
Atmosphere Model

Abstract The impacts of environmental aerosols on the growth of an extratropical cyclone in a realistic winter flow setting are investigated using the superparameterized Community Atmosphere Model (SP-CAM) where cloud-scale dynamics and thermodynamics are explicitly resolved. An examination of the results from 13 ensemble pairs suggests that the growth rate of the cyclone is temporarily reduced as a result of increased aerosol concentrations. A convection–advection–moisture self-adjustment (CAMS) mechanism of aerosol–cyclone interaction is proposed to explain this finding. Specifically, the weakened growth is unambiguously attributed to the weakening of the cold advection underneath the midtropospheric trough of the cyclone. The weakened cold advection is in turn driven by a decrease of the zonal temperature gradient that is tied to the reduced latent heating in the stratiform cloud region of the cyclone. Invigoration of convection ahead of the cold front by aerosols is found to be directly responsible for a suppressed moisture supply into the stratiform cloud region and thus the reduced latent heating there. The regional climate implications of these results are discussed. Also highlighted is the importance of incorporating aerosol microphysical effects on deep convection in any modeling effort that aims to understand aerosol–circulation interaction at the extratropics.

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