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 is currently available in two primary versions. The public version is accessible to other researchers and adheres closely to the model described in the original paper. It uses a Cartesian grid with constant horizontal spacing and variable vertical spacing. Although this version remains largely faithful to the initial model description, numerous modifications have been made to its physical properties. Recently, an extended version of SAM has been developed and distributed among various modeling groups. This version introduces several enhancements over the public model. The most significant change occurred in 2017 when SAM was adapted to a longitude-latitude grid, enabling it to simulate conditions on Earth. Additionally, it now incorporates features such as topography and buildings. This version is referred to as Global SAM, or gSAM, and described by Khairoutdinov et al (2022).

Model Highlights