System for Atmospheric Modeling

Model History

The System for Atmospheric Modeling, or SAM, has evolved from the Large-Eddy Simulation (LES) model that I coded for a class project while being a Ph.D. student at the University of Oklahoma. Coupled with the explicit or bin microphysics of Yefim Kogan, my Ph.D. advisor, the model has become a useful tool to study detailed cloud processes in the stratocumulus-topped boundary layers (Khairoutdinov and Kogan 1999). As part of my Ph.D thesis, I used the model to develop a bulk microphysics scheme for drizzling PBL clouds, a so-called KK scheme, which has been used in many models as parameterization of autoconversion in warm clouds (Khairoutdinov and Kogan 2000).

Right after completing my PhD studies, in January 1998, I started my work at the Department of Atmospheric Science, Colorado State University, in David Randall's research group. At CSU, the model has undergone major overhaul, both of code and physics. The bin warm-cloud microphysics has been replaced with bulk microphysics that included ice processes. The Bussinesq approximation was changed to anelastic, which allowed to simulate deep convection. The most important change though was to make the model suitable to run on massively parallel computers by using horizontal domain decomposition and employing the MPI communication protocol. The original model has been documented by Khairoutdinov and Randall (2003). In the same year, the model received its official name - SAM - with the version count starting from 6.0, reflecting the fact that SAM represents the sixth cloud-model design since 1987 when I started cloud modeling career at the Central Aerological Observatory (CAO) in the USSR.

Today, SAM is used by dozens cloud modelers in the United States and beyond. Incomplete list of publications of the scientific results obtained using SAM can be found at the end of this page.
SAM currently exists in two major versions. The public version is available for other researchers. It is formulated on the original Cartesian grid, with constant horizontal and variable vertical spacing. The public model follows rather closely the aferomentioned model-description paper, although many changes have been made to the model physics.

Another version is for my own use only and it is not shared with other modeling groups (yet), although many improvements to the public version have come from this experimental version. The fundamental change to the model occured in 2017, when the model formulation has been generalized to longitude-latitude grid to be able to simulate Earth. This version of SAM is currently called Global SAM, or GSAM. The GSAM description paper is currently in preparation.

Model Highlights