The University of Washington Shallow Convection and Moist Turbulence Schemes and Their Impact on Climate Simulations with the Community Atmosphere Model

2009 ◽  
Vol 22 (12) ◽  
pp. 3449-3469 ◽  
Author(s):  
Sungsu Park ◽  
Christopher S. Bretherton
Keyword(s):  
Radiative Forcing ◽  
Mean Squared Error ◽  
Global Climate Models ◽  
Cumulus Parameterization ◽  
Vertical Resolution ◽  
Shallow Convection ◽  
University Of Washington ◽  
Community Atmosphere Model ◽  
Atmosphere Model ◽  
The University

Abstract This paper describes a new version of the University of Washington shallow cumulus parameterization. The new version includes improved treatments of lateral mixing rates into cumulus updrafts, the evaporation of precipitation and of the interaction of cumuli with the underlying subcloud layer, and a treatment of the convective inhibition-based mass-flux closure that is more numerically stable and is suitable for the long time steps of global climate models. The paper also documents its performance when combined with a new moist turbulence parameterization in simulations with version 3.5 of the Community Atmosphere Model (CAM3.5). A single-column simulation of nonprecipitating trade cumulus shows considerable improvements in vertical thermodynamic structure and less resolution sensitivity in the new schemes compared to CAM3.5. In global simulations, the new schemes, combined with an increase of vertical resolution from 26 to 30 levels, produce a significant (7%) reduction in overall climate bias, calculated from root-mean-squared error of the seasonal model climatology compared to a suite of global observations of various fields. Biases in almost all fields, particularly the shortwave cloud radiative forcing, are reduced. Geographical bias patterns in surface rainfall, liquid water path, and surface air temperature are only mildly affected by the model parameterization and vertical resolution changes.

The Evolution of Climate Sensitivity and Climate Feedbacks in the Community Atmosphere Model

2012 ◽  
Vol 25 (5) ◽  
pp. 1453-1469 ◽  
Author(s):  
A. Gettelman ◽  
J. E. Kay ◽  
K. M. Shell
Keyword(s):  
Climate Sensitivity ◽  
Radiative Forcing ◽  
Ocean Model ◽  
Lapse Rate ◽  
Shallow Convection ◽  
Climate Feedbacks ◽  
Cloud Feedbacks ◽  
Community Atmosphere Model ◽  
Atmosphere Model ◽  
The Difference

The major evolution of the National Center for Atmospheric Research Community Atmosphere Model (CAM) is used to diagnose climate feedbacks, understand how climate feedbacks change with different physical parameterizations, and identify the processes and regions that determine climate sensitivity. In the evolution of CAM from version 4 to version 5, the water vapor, temperature, surface albedo, and lapse rate feedbacks are remarkably stable across changes to the physical parameterization suite. However, the climate sensitivity increases from 3.2 K in CAM4 to 4.0 K in CAM5. The difference is mostly due to (i) more positive cloud feedbacks and (ii) higher CO2 radiative forcing in CAM5. The intermodel differences in cloud feedbacks are largest in the tropical trade cumulus regime and in the midlatitude storm tracks. The subtropical stratocumulus regions do not contribute strongly to climate feedbacks owing to their small area coverage. A “modified Cess” configuration for atmosphere-only model experiments is shown to reproduce slab ocean model results. Several parameterizations contribute to changes in tropical cloud feedbacks between CAM4 and CAM5, but the new shallow convection scheme causes the largest midlatitude feedback differences and the largest change in climate sensitivity. Simulations with greater cloud forcing in the mean state have lower climate sensitivity. This work provides a methodology for further analysis of climate sensitivity across models and a framework for targeted comparisons with observations that can help constrain climate sensitivity to radiative forcing.

Exposing Global Cloud Biases in the Community Atmosphere Model (CAM) Using Satellite Observations and Their Corresponding Instrument Simulators

2012 ◽  
Vol 25 (15) ◽  
pp. 5190-5207 ◽  
Author(s):  
J. E. Kay ◽  
B. R. Hillman ◽  
S. A. Klein ◽  
Y. Zhang ◽  
B. Medeiros ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Marine Boundary Layer ◽  
Climate Model ◽  
Substantial Improvement ◽  
Satellite Observations ◽  
Cloud Properties ◽  
Community Atmosphere Model ◽  
Realistic Representation ◽  
Model Cloud ◽  
Atmosphere Model

Abstract Satellite observations and their corresponding instrument simulators are used to document global cloud biases in the Community Atmosphere Model (CAM) versions 4 and 5. The model–observation comparisons show that, despite having nearly identical cloud radiative forcing, CAM5 has a much more realistic representation of cloud properties than CAM4. In particular, CAM5 exhibits substantial improvement in three long-standing climate model cloud biases: 1) the underestimation of total cloud, 2) the overestimation of optically thick cloud, and 3) the underestimation of midlevel cloud. While the increased total cloud and decreased optically thick cloud in CAM5 result from improved physical process representation, the increased midlevel cloud in CAM5 results from the addition of radiatively active snow. Despite these improvements, both CAM versions have cloud deficiencies. Of particular concern, both models exhibit large but differing biases in the subtropical marine boundary layer cloud regimes that are known to explain intermodel differences in cloud feedbacks and climate sensitivity. More generally, this study demonstrates that simulator-facilitated evaluation of cloud properties, such as amount by vertical level and optical depth, can robustly expose large and at times radiatively compensating climate model cloud biases.

scholarly journals Modeling dust as component minerals in the Community Atmosphere Model: development of framework and impact on radiative forcing

2014 ◽  
Vol 14 (12) ◽  
pp. 17749-17816 ◽  
Author(s):  
R. A. Scanza ◽  
N. Mahowald ◽  
S. Ghan ◽  
C. S. Zender ◽  
J. F. Kok ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Climate Models ◽  
Mineral Soil ◽  
Model Development ◽  
Spatial And Temporal Variability ◽  
Model Version ◽  
Mineral Aerosols ◽  
Community Atmosphere Model ◽  
Atmosphere Model ◽  
Aerosol Module

Abstract. The mineralogy of desert dust is important due to its effect on radiation, clouds and biogeochemical cycling of trace nutrients. This study presents the simulation of dust radiative forcing as a function of both mineral composition and size at the global scale using mineral soil maps for estimating emissions. Externally mixed mineral aerosols in the bulk aerosol module in the Community Atmosphere Model version 4 (CAM4) and internally mixed mineral aerosols in the modal aerosol module in the Community Atmosphere Model version 5.1 (CAM5) embedded in the Community Earth System Model version 1.0.5 (CESM) are speciated into common mineral components in place of total dust. The simulations with mineralogy are compared to available observations of mineral atmospheric distribution and deposition along with observations of clear-sky radiative forcing efficiency. Based on these simulations, we estimate the all-sky direct radiative forcing at the top of the atmosphere as +0.05 W m−2 for both CAM4 and CAM5 simulations with mineralogy and compare this both with simulations of dust in release versions of CAM4 and CAM5 (+0.08 and +0.17 W m−2) and of dust with optimized optical properties, wet scavenging and particle size distribution in CAM4 and CAM5, −0.05 and −0.17 W m−2, respectively. The ability to correctly include the mineralogy of dust in climate models is hindered by its spatial and temporal variability as well as insufficient global in-situ observations, incomplete and uncertain source mineralogies and the uncertainties associated with data retrieved from remote sensing methods.

scholarly journals Higher-Order Turbulence Closure and Its Impact on Climate Simulations in the Community Atmosphere Model

2013 ◽  
Vol 26 (23) ◽  
pp. 9655-9676 ◽  
Author(s):  
Peter A. Bogenschutz ◽  
Andrew Gettelman ◽  
Hugh Morrison ◽  
Vincent E. Larson ◽  
Cheryl Craig ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Higher Order ◽  
Turbulence Closure ◽  
Trade Wind ◽  
Gradual Transition ◽  
Shallow Convection ◽  
Boundary Layer Clouds ◽  
Community Atmosphere Model ◽  
Climate Simulations ◽  
Atmosphere Model

This paper describes climate simulations of the Community Atmosphere Model, version 5 (CAM5), coupled with a higher-order turbulence closure known as Cloud Layers Unified by Binormals (CLUBB). CLUBB is a unified parameterization of the planetary boundary layer (PBL) and shallow convection that is centered around a trivariate probability density function (PDF) and replaces the conventional PBL, shallow convection, and cloud macrophysics schemes in CAM5. CAM–CLUBB improves many aspects of the base state climate compared to CAM5. Chief among them is the transition of stratocumulus to trade wind cumulus regions in the subtropical oceans. In these regions, CAM–CLUBB provides a much more gradual transition that is in better agreement with observational analysis compared to CAM5, which is too abrupt. The improvement seen in CAM–CLUBB can be largely attributed to the gradual evolution of the simulated turbulence, which is in part a result of the unified nature of the parameterization, and to the general improved representation of shallow cumulus clouds compared to CAM5. In addition, there are large differences in the representation and structure of marine boundary layer clouds between CAM–CLUBB and CAM5. CAM–CLUBB is also shown to be more robust, in terms of boundary layer clouds, to changes in vertical resolution for global simulations in a preliminary test.

scholarly journals Monsoon sensitivity to aerosol direct radiative forcing in the community atmosphere model

2012 ◽  
Vol 121 (4) ◽  
pp. 867-889 ◽  
Author(s):  
S SAJANI ◽  
K KRISHNA MOORTHY ◽  
K RAJENDRAN ◽  
RAVI S NANJUNDIAH
Keyword(s):  
Radiative Forcing ◽  
Community Atmosphere Model ◽  
Direct Radiative Forcing ◽  
Atmosphere Model

The Formulation and Atmospheric Simulation of the Community Atmosphere Model Version 3 (CAM3)

2006 ◽  
Vol 19 (11) ◽  
pp. 2144-2161 ◽  
Author(s):  
William D. Collins ◽  
Philip J. Rasch ◽  
Byron A. Boville ◽  
James J. Hack ◽  
James R. McCaa ◽  
...  
Keyword(s):  
Finite Volume ◽  
Radiative Forcing ◽  
General Circulation ◽  
Circulation Model ◽  
Surface Radiation ◽  
Time Step ◽  
Community Land Model ◽  
Enso Events ◽  
Community Atmosphere Model ◽  
Atmosphere Model

Abstract A new version of the Community Atmosphere Model (CAM) has been developed and released to the climate community. CAM Version 3 (CAM3) is an atmospheric general circulation model that includes the Community Land Model (CLM3), an optional slab ocean model, and a thermodynamic sea ice model. The dynamics and physics in CAM3 have been changed substantially compared to implementations in previous versions. CAM3 includes options for Eulerian spectral, semi-Lagrangian, and finite-volume formulations of the dynamical equations. It supports coupled simulations using either finite-volume or Eulerian dynamics through an explicit set of adjustable parameters governing the model time step, cloud parameterizations, and condensation processes. The model includes major modifications to the parameterizations of moist processes, radiation processes, and aerosols. These changes have improved several aspects of the simulated climate, including more realistic tropical tropopause temperatures, boreal winter land surface temperatures, surface insolation, and clear-sky surface radiation in polar regions. The variation of cloud radiative forcing during ENSO events exhibits much better agreement with satellite observations. Despite these improvements, several systematic biases reduce the fidelity of the simulations. These biases include underestimation of tropical variability, errors in tropical oceanic surface fluxes, underestimation of implied ocean heat transport in the Southern Hemisphere, excessive surface stress in the storm tracks, and offsets in the 500-mb height field and the Aleutian low.

scholarly journals Unified parameterization of the planetary boundary layer and shallow convection with a higher-order turbulence closure in the Community Atmosphere Model: single-column experiments

2012 ◽  
Vol 5 (6) ◽  
pp. 1407-1423 ◽  
Author(s):  
P. A. Bogenschutz ◽  
A. Gettelman ◽  
H. Morrison ◽  
V. E. Larson ◽  
D. P. Schanen ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Higher Order ◽  
Turbulence Closure ◽  
Shallow Convection ◽  
Liquid Water Path ◽  
Community Atmosphere Model ◽  
Single Column ◽  
Atmosphere Model ◽  
Similar Accuracy

Abstract. This paper describes the coupling of the Community Atmosphere Model (CAM) version 5 with a unified multi-variate probability density function (PDF) parameterization, Cloud Layers Unified by Binormals (CLUBB). CLUBB replaces the planetary boundary layer (PBL), shallow convection, and cloud macrophysics schemes in CAM5 with a higher-order turbulence closure based on an assumed PDF. Comparisons of single-column versions of CAM5 and CAM-CLUBB are provided in this paper for several boundary layer regimes. As compared to large eddy simulations (LESs), CAM-CLUBB and CAM5 simulate marine stratocumulus regimes with similar accuracy. For shallow convective regimes, CAM-CLUBB improves the representation of cloud cover and liquid water path (LWP). In addition, for shallow convection CAM-CLUBB offers better fidelity for subgrid-scale vertical velocity, which is an important input for aerosol activation. Finally, CAM-CLUBB results are more robust to changes in vertical and temporal resolution when compared to CAM5.

scholarly journals PORT, a CESM tool for the diagnosis of radiative forcing

2012 ◽  
Vol 5 (3) ◽  
pp. 2687-2704 ◽  
Author(s):  
A. J. Conley ◽  
J.-F. Lamarque ◽  
F. Vitt ◽  
W. D. Collins ◽  
J. Kiehl
Keyword(s):  
Carbon Dioxide ◽  
Radiative Transfer ◽  
Ozone Concentration ◽  
Radiative Forcing ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Community Atmosphere Model ◽  
Community Earth System Model ◽  
Atmosphere Model

Abstract. The Parallel Offline Radiative Transfer (PORT) model is a tool for diagnosing radiative forcing. It isolates the radiation code from the Community Atmosphere Model (CAM4) in the Community Earth System Model (CESM1). The computation of radiative forcing from doubling of carbon dioxide and from the change of ozone concentration from year 1850 to 2000 illustrates the use of PORT.

Sign in / Sign up

Export Citation Format

Share Document