Overview

Important

The CAM Reference Manual is more comprehensive than the current CESM2.X documentation. It even says, “This manual is intended for anyone who plans to get their hands dirty modifying CAM code.”

For example, this CESM1.2 Physics Driver page in the reference manual doesn’t seem to have an analog in the CESM2.X documentation.

Nomenclature

CAM distinguishes between Dynamical cores and Physics packages. State variables are updated first by the dynamics and then by the physics. Both the dynamical cores and the physics packages are implemented in a modular fashion and plug into the model infrastructure using an interface.

Dynamical cores

Dynamical cores are numerical methods implemented on specific model grids that simulate the large scale atmospheric flow. CAM supports several dynamical cores including the:

• EUL (Eulerian spectral-transform)

• SLD (semi-Lagrangian spectral-transform)

• FV (finite-volume)

• SE (spectral-elements)

Physics packages

Physics packages implement parameterized physical processes within a single column of the model grid. This functionality is often called a vertical solver within the space weather community.

Kalnay et al. (1989) 1 describe eleven rules to ensure physics package interoperability. Packages should only be responsible for performing a calculation upon either a single column or a limited section of the model’s state. Other aspects of model integration such as communication, parallelization, input and output are handled by the support infrastructure within the model.

These standards allow for modularity and were developed in response to the difficulty of inserting and comparing physics schemes into a given model.

Coding standards

CAM doesn’t have a strict set of coding standards because much of its source code was contributed by the community. However, the UCAR wiki has a draft of coding standards for CAM. The document nodes that most of the code is preprocessed with Fortran preprocessor, fpp, which is not officially a part of the Fortran language standard.

Directory structure

This collection contains pages corresponding to each of the subdirectories in cesm/components/cam/src/ that describes what each of the subdirectories contains.

• advection

• atmos_phys

• chemistry

• control

• cpl

• dynamics

• ionosphere

• Overview

• physics

• unit_drivers

• utils

References

1

Kalnay, E., M. Kanamitsu, J. Pfaendtner, J. Sela, M. Suarez, J. Stackpole, J. Tuccillo, L. Umscheid, and D. Williamson., 1989: Rules for Interchange of Physical Parameterizations. Bulletin of the American Meteorological Society, 70, 620–622, https://journals.ametsoc.org/view/journals/bams/70/6/1520-0477_1989_070_0620_rfiopp_2_0_co_2.xml.