This computation involved: CAM 3.5 - Interim version of the NCAR Community Atmospheric Model deployed on National Centre for Atmospheric Research (USA) computing facility. The CAM3.5 (NCAR Community Atmosphere Model, version 3.5) is a atmospheric model developed by the NCAR in collaboration with the climate modelling community.

This version is the recently improved version of the state-of-the-art atmospheric general circulation model (AGCM) and serves as an interim version in the process of improving the model physics for the next-generation CAM, version 4 (CAM4), which is a global primitive-equation model with 26 vertical levels.

The version 3.5 of the CAM model is closely related to the previous CAM 3.0 version. Main modifications include changes to:
- convective and cloud processes; the calculation of cloud fraction is updated
- the land model: new hydrology, surface datasets an canopy integration were introduced.
- chemistry modules

The above changes are documented in Oleson et al. 2008; Stockli et al. 2008; Neale et al. 2008; Richter and Rasch 2008; Gent et al. 2009; Chen et al. 2010.

The horizontal and vertical representation, resolution and parameterization characteristics are in CAM3.0 as follows (2009):

A. Atmosphere
- resolution
- Horizontal :
For spectral dynamics the horizonal grid is Gaussian and is specified as nlat x nlon where nlat is the number of Gaussian latitudes and nlon is the number of distinct longitudes. For finite-volume dynamics the meridional grid is equally spaced and includes the pole points. It is specified as dlatxdlon where dlat is the latitude cell size and dlon is the longitude cell size, both in degrees. All of the valid resolutions are listed in the resolution_parameters.xml file in the configuration script directory. Commonly used resolutions include 48x96, 64x128, and 128x256 for the spectral dynamic cores, and 2x2.5 for the Finite-Volume dynamic core.
- Vertical :
Hybrid sigma-pressure. 26 levels.

More details on the theoretical nature of the vertical coordinate system can be found in Collins et al. (2004).

- parametrizations
The CAM 3.0 cleanly separates the parameterization suite from the dynamical core, and makes it easier to replace or modify each in isolation. The dynamical core can be coupled to the parameterization suite in a purely time split manner or in a purely process split one. The Process Split form is convenient for spectral transform models. With Time Split approximations extra spectral transforms are required to convert the updated momentum variables provided by the parameterizations to vorticity and divergence for the Eulerian spectral core, or to recalculate the temperature gradient for the semi-Lagrangian spectral core. The Time Split form is convenient for the finite-volume core which adopts a Lagrangian vertical coordinate. Since the scheme is explicit and restricted to small time-steps by its non-advective component, it sub-steps the dynamics multiple times during a longer parameterization time step. With Process Split approximations the forcing terms must be interpolated to an evolving Lagrangian vertical coordinate every sub-step of the dynamical core. Besides the expense involved, it is not completely obvious how to interpolate the parameterized forcing, which can have a vertical grid scale component arising from vertical grid scale clouds, to a different vertical grid. More about Process Split and Time Split approximations is explained in Williamson (2002)

The total parameterization package in CAM 3.0 consists of a sequence of components, indicated by

$\displaystyle P = { M,R,S,T }

where
M denotes (Moist) precipitation processes,
R denotes clouds and Radiation,
S denotes the Surface model, and
T denotes Turbulent mixing.

Each of these in turn is subdivided into various components:
M includes an optional dry adiabatic adjustment (normally applied only in the stratosphere), moist penetrative convection, shallow convection, and large-scale stable condensation;
R first calculates the cloud parameterization followed by the radiation parameterization;
S provides the surface fluxes obtained from land, ocean and sea ice models, or calculates them based on specified surface conditions such as sea surface temperatures and sea ice distribution. These surface fluxes provide lower flux boundary conditions for the turbulent mixing
T which is comprised of the planetary boundary layer parameterization, vertical diffusion, and gravity wave drag.

See linked documentation for further details on the parameterisation schemes.

More on NCAR Community Atmosphere Model (CAM3) can be found in the online documentation links attached to this record.

NCAR’s (National Centre for Atmospheric Research) supercomputing resources serve nearly 1,300 users in a wide variety of disciplines including climatology, meteorology, oceanography, astrophysics, fluid dynamics, and turbulence. In particular, CISL (Computational Information Systems Laboratory) provisions a balanced suite of high-performance resources that allows today’s Earth System models to simulate atmosphere, ocean, sea ice, and land surface processes with increasing fidelity.