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 The E3SM version 1 single-column model

2020 ◽  
Vol 13 (9) ◽  
pp. 4443-4458
Author(s):  
Peter A. Bogenschutz ◽  
Shuaiqi Tang ◽  
Peter M. Caldwell ◽  
Shaocheng Xie ◽  
Wuyin Lin ◽  
...  
Keyword(s):  
General Circulation ◽  
Model Development ◽  
Circulation Model ◽  
System Model ◽  
Earth System ◽  
Efficient Tool ◽  
Column Model ◽  
Community Atmosphere Model ◽  
Single Column ◽  
Single Column Model

Abstract. The single-column model (SCM) functionality of the Energy Exascale Earth System Model version 1 (E3SMv1) is described in this paper. The E3SM SCM was adopted from the SCM used in the Community Atmosphere Model (CAM) but has evolved significantly since then. We describe changes made to the aerosol specification in the SCM, idealizations, and developments made so that the SCM uses the same dynamical core as the full general circulation model (GCM) component. Based on these changes, we describe and demonstrate the seamless capability to “replay” a GCM column using the SCM. We give an overview of the E3SM case library and briefly describe which cases may serve as useful proxies for replicating and investigate some long-standing biases in the full GCM runs while demonstrating that the E3SM SCM is an efficient tool for both model development and evaluation.

scholarly journals Resolved Snowball Earth Clouds

2014 ◽  
Vol 27 (12) ◽  
pp. 4391-4402 ◽  
Author(s):  
Dorian S. Abbot
Keyword(s):  
Radiative Forcing ◽  
General Circulation ◽  
Circulation Model ◽  
Cloud Amount ◽  
Cloud Microphysics ◽  
Snowball Earth ◽  
Geochemical Data ◽  
Microphysics Scheme ◽  
Cloud Resolving Model ◽  
Cloud Ice

Abstract Recent general circulation model (GCM) simulations have challenged the idea that a snowball Earth would be nearly entirely cloudless. This is important because clouds would provide a strong warming to a high-albedo snowball Earth. GCM results suggest that clouds could lower the threshold CO2 needed to deglaciate a snowball by a factor of 10–100, enough to allow consistency with geochemical data. Here a cloud-resolving model is used to investigate cloud and convection behavior in a snowball Earth climate. The model produces convection that extends vertically to a similar temperature as modern tropical convection. This convection produces clouds that resemble stratocumulus clouds under an inversion on modern Earth, which slowly dissipate by sedimentation of cloud ice. There is enough cloud ice for the clouds to be optically thick in the longwave, and the resulting cloud radiative forcing is similar to that produced in GCMs run in snowball conditions. This result is robust to large changes in the cloud microphysics scheme because the cloud longwave forcing, which dominates the total forcing, is relatively insensitive to cloud amount and particle size. The cloud-resolving model results are therefore consistent with the idea that clouds would provide a large warming to a snowball Earth, helping to allow snowball deglaciation.

scholarly journals Introduction of prognostic rain in ECHAM5: design and single column model simulations

2008 ◽  
Vol 8 (11) ◽  
pp. 2949-2963 ◽  
Author(s):  
R. Posselt ◽  
U. Lohmann
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Cloud Microphysics ◽  
Rain Water ◽  
Time Step ◽  
Surface Precipitation ◽  
Column Model ◽  
Single Column ◽  
Single Column Model

Abstract. Prognostic equations for the rain mass mixing ratio and the rain drop number concentration are introduced into the large-scale cloud microphysics parameterization of the ECHAM5 general circulation model (ECHAM5-PROG). To this end, a rain flux from one level to the next with the appropriate fall speed is introduced. This maintains rain water in the atmosphere to be available for the next time step. Rain formation in ECHAM5-PROG is, therefore, less dependent on the autoconversion rate than the standard ECHAM5 but shifts the emphasis towards the accretion rates in accordance with observations. ECHAM5-PROG is tested and evaluated with Single Column Model (SCM) simulations for two cases: the marine stratocumulus study EPIC (October 2001) and the continental mid-latitude ARM Cloud IOP (shallow frontal cloud case – March 2000). In case of heavy precipitation events, the prognostic equations for rain hardly affect the amount and timing of precipitation at the surface in different SCM simulations because heavy rain depends mainly on the large-scale forcing. In case of thin, drizzling clouds (i.e., stratocumulus), surface precipitation is sensitive to the number of sub-time steps used in the prognostic rain scheme. Cloud microphysical quantities, such as cloud liquid and rain water within the atmosphere, are sensitive to the number of sub-time steps in both considered cases. This results from the decreasing autoconversion rate and increasing accretion rate.

scholarly journals Introduction of prognostic rain in ECHAM5: design and Single Column Model simulations

2007 ◽  
Vol 7 (5) ◽  
pp. 14675-14706 ◽  
Author(s):  
R. Posselt ◽  
U. Lohmann
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Cloud Microphysics ◽  
Rain Water ◽  
Time Step ◽  
Surface Precipitation ◽  
Column Model ◽  
Single Column ◽  
Single Column Model

Abstract. Prognostic equations for the rain mass mixing ratio and the rain drop number concentration are introduced into the large-scale cloud microphysics parameterization of the ECHAM5 general circulation model (ECHAM5-RAIN). For this a rain flux from one level to the next with the appropriate fall speed is introduced. This maintains rain water in the atmosphere to be available for the next time step. Rain formation in ECHAM5-RAIN is, therefore, less dependent on the autoconversion rate than the standard ECHAM5 but shifts the emphasis towards the accretion rates in accordance with observations. ECHAM5-RAIN is tested and evaluated with two cases: the continental mid-latitude ARM Cloud IOP (shallow frontal cloud case – March 2000) and EPIC (a marine stratocumulus study – October 2001). The prognostic equations for rain hardly affect the amount and timing of precipitation at the surface in different Single Column Model (SCM) simulations for heavy precipitating clouds because heavy rain depends mainly on the large-scale forcing. In case of thin, drizzling clouds (i.e., stratocumulus), an increase in surface precipitation is caused by more sub-time steps used in the prognostic rain scheme until convergence is reached. Cloud microphysical quantities, such as liquid and rain water, are more sensitive to the number of sub-time steps for light precipitation. This results from the decreasing autoconversion rate and increasing accretion rate.

scholarly journals The E3SM version 1 Single Column Model

2020 ◽  
Author(s):  
Peter A. Bogenschutz ◽  
Shuaiqi Tang ◽  
Peter M. Caldwell ◽  
Shaocheng Xie ◽  
Wuyin Lin ◽  
...  
Keyword(s):  
General Circulation ◽  
Model Development ◽  
Circulation Model ◽  
System Model ◽  
Earth System ◽  
Efficient Tool ◽  
Column Model ◽  
Community Atmosphere Model ◽  
Single Column ◽  
Single Column Model

Abstract. The single column model (SCM) functionality of the Energy Exascale Earth System Model version 1 (E3SMv1) is described in this paper. The E3SM SCM was adopted from the SCM used in the Community Atmosphere Model (CAM), but has evolved significantly since then. We describe changes made to the aerosol specification in the SCM, idealizations, and developments made so that the SCM uses the same dynamical core as the full general circulation model (GCM) component. Based on these changes, we describe and demonstrate the seamless capability to ``replay" a GCM column using the SCM. We give an overview of the E3SM case library and briefly describe which cases may serve as useful proxies for replicating and investigate some long standing biases in the full GCM runs, while demonstrating that the E3SM SCM is an efficient tool for both model development and evaluation.

scholarly journals Aerosol specification in single-column Community Atmosphere Model version 5

2015 ◽  
Vol 8 (3) ◽  
pp. 817-828 ◽  
Author(s):  
B. Lebassi-Habtezion ◽  
P. M. Caldwell
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Climate Models ◽  
Model Development ◽  
Circulation Model ◽  
Cloud Droplet ◽  
Global Mode ◽  
Community Atmosphere Model ◽  
Single Column ◽  
Atmosphere Model

Abstract. Single-column model (SCM) capability is an important tool for general circulation model development. In this study, the SCM mode of version 5 of the Community Atmosphere Model (CAM5) is shown to handle aerosol initialization and advection improperly, resulting in aerosol, cloud-droplet, and ice crystal concentrations which are typically much lower than observed or simulated by CAM5 in global mode. This deficiency has a major impact on stratiform cloud simulations but has little impact on convective case studies because aerosol is currently not used by CAM5 convective schemes and convective cases are typically longer in duration (so initialization is less important). By imposing fixed aerosol or cloud-droplet and crystal number concentrations, the aerosol issues described above can be avoided. Sensitivity studies using these idealizations suggest that the Meyers et al. (1992) ice nucleation scheme prevents mixed-phase cloud from existing by producing too many ice crystals. Microphysics is shown to strongly deplete cloud water in stratiform cases, indicating problems with sequential splitting in CAM5 and the need for careful interpretation of output from sequentially split climate models. Droplet concentration in the general circulation model (GCM) version of CAM5 is also shown to be far too low (~ 25 cm−3) at the southern Great Plains (SGP) Atmospheric Radiation Measurement (ARM) site.

The General Circulation and Robust Relative Humidity

2006 ◽  
Vol 19 (24) ◽  
pp. 6278-6290 ◽  
Author(s):  
S. C. Sherwood ◽  
C. L. Meyer
Keyword(s):  
Relative Humidity ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Cloud Microphysics ◽  
Homogeneous State ◽  
Surface Warming ◽  
Westerly Jet ◽  
Community Atmosphere Model ◽  
Microphysical Processes

Abstract The sensitivity of free-tropospheric relative humidity to cloud microphysics and dynamics is explored using a simple 2D humidity model and various configurations of the National Center for Atmospheric Research (NCAR) Community Atmosphere Model version 3 (CAM3) atmospheric general circulation model (AGCM). In one configuration the imposed surface temperatures and radiative perturbations effectively eliminated the Hadley and Walker circulations and the main westerly jet, creating instead a homogeneous “boiling kettle” world in low and midlatitudes. A similarly homogeneous state was created in the 2D model by rapid horizontal mixing. Relative humidity ℛ simulated by the AGCM was insensitive to surface warming. Doubling a parameter governing cloud water reevaporation increased tropical mean ℛ near the midtroposphere by about 4% with a realistic circulation, but by more than 10% in the horizontally homogeneous states. This was consistent in both models. AGCM microphysical sensitivity decreased in the upper troposphere, and vanished outside the Tropics. Convective organization by the general circulation evidently makes relative humidity much more robust to microphysical details by concentrating the rainfall in moist environments. Models that fail to capture this will overestimate the microphysical sensitivity of humidity. Based on these results, the uncertainty in the strength of the water vapor feedback associated with cloud microphysical processes seems unlikely to exceed a few percent. This does not include uncertainties associated with large-scale dynamics or cloud radiative effects, which cannot be quantified, although radical CAM3 circulation changes reported here had surprisingly little impact on simulated relative humidity.

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