Integrating Cloud Processes in the Community Atmosphere Model, Version 5

Abstract

This paper provides a description of the integrated representation for the cloud processes in the Community Atmosphere Model, version 5 (CAM5). CAM5 cloud parameterizations add the following unique characteristics to previous versions: 1) a cloud macrophysical structure with horizontally nonoverlapped deep cumulus, shallow cumulus, and stratus in each grid layer, where each of which has its own cloud fraction, and mass and number concentrations for cloud liquid droplets and ice crystals; 2) stratus–radiation–turbulence interactions that allow CAM5 to simulate marine stratocumulus solely from grid-mean relative humidity without relying on a stability-based empirical formula; 3) prognostic treatment of the number concentrations of stratus liquid droplets and ice crystals, with activated aerosols and detrained in-cumulus condensates as the main sources and with evaporation, sedimentation, and precipitation of stratus condensate as the main sinks; and 4) radiatively active cumulus and snow. By imposing consistency between diagnosed stratus fraction and prognosed stratus condensate, unrealistically empty or highly dense stratus is avoided in CAM5. Because of the activation of the prognostic aerosols and the parameterizations of the radiation and stratiform precipitation production as a function of the cloud droplet size, CAM5 simulates various aerosol indirect effects as well as the direct effects: that is, aerosols affect both the radiation budget and the hydrological cycle. Detailed analysis of various simulations indicates that CAM5 improves upon CAM3/CAM4 in global performance as well as in physical formulation. However, several problems are also identified in CAM5, which can be attributed to deficient regional tuning, inconsistency between various physics parameterizations, and incomplete treatment of physics. Efforts are continuing to further improve CAM5.

Impacts of absorbing aerosol deposition on snowpack and hydrologic cycle in the Rocky Mountain region based on variable-resolution CESM (VR-CESM) simulations

“…The CAM5 physics suite consists of shallow convection (Park and Bretherton, 2009), deep convection (Zhang and McFarlane, 1995;Richter and Rasch, 2008), cloud microphysics (Morrison and Gettelman, 2008) and macrophysics (Park et al, 2014), radiation (Iacono et al, 2008), and aerosols . For aerosols, a modal aerosol module (MAM) is adopted to represent the internal and external mixing of aerosol components such as BC, OC, sulfate, ammonium, sea salt, and mineral dust .…”

Impact of moisture divergence on systematic errors in precipitation around the Tibetan Plateau in a general circulation model

“…CAM5 is a component of the Community Earth System Model (CESM) (Zhang and McFarlane 1995;Richter and Rasch 2008;Neale et al 2008). CAM5 features (1) a new shallow convection scheme and a new moist turbulence scheme ) developed by the University of Washington ; (2) a two-moment cloud microphysics scheme Gettelman et al 2008) and a cloud macrophysics scheme (Park et al 2014) for the parameterizations of clouds; and (3) an open source Rapid Radiative Transfer Model for GCM (RRTMG) package developed by the Atmospheric and Environmental Research (AER) incorporation is used as the radiation module (Mlawer et al 1997;Iacono et al 2008). A new modal aerosol module is also implemented in CAM5 (Liu et al 2012).…”

Characterization and Modeling of Fog in the Mexico Basin

“…On the other hand, the CAM 5.1 scheme shows to be more appropriate for radiation fog simulation, the reason being that it allows for the tuning of threshold relative humidity for low and high clouds (78.75% and 80% were set over land without snow, respectively), and interpolated thresholds for the mid-level clouds. In this way, this parameterization produces condensation and evaporation for subgrid clouds with changing cloud fraction (Rasch and Kristjánsson, 1998;Park et al, 2014), even if the subgrid is sub-saturated (Ma et al, 2014). As for the PBL schemes, the QNSE uses a theory of turbulence with stable and weakly unstable stratification that accommodates the stratification-induced disparity between the transport processes in the horizontal and vertical directions, and accounts for the combined effect of turbulence and waves.…”