System For Atmospheric Modeling

Model History

The System for Atmospheric Modeling, or SAM, evolved from the Large-Eddy Simulation (LES) model, coded by Dr. Marat Khairoutdinov while a Ph.D. student at the University of Oklahoma. Coupled with the explicit or bin microphysics of Yefim Kogan, his 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). The model was used to develop a bulk microphysics scheme for drizzling PBL clouds (Khairoutdinov and Kogan 2000).

In January 1998, Dr. Khairoutdinov started at the Department of Atmospheric Science, Colorado State University in David Randall’s research group. At CSU, the model code and physics were overhauled. The explicit warm-cloud microphysics has been replaced with the bulk microphysics that included the ice-microphysics processes. The thermodynamic prognostic variables have also been changed. The model has become suitable to run on massively parallel computers by using horizontal domain decomposition and employing the MPI communication protocol. The model’s details can be found in Khairoutdinov and Randall (2003). In 2003, 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 Dr. Khairoutdinov started his cloud modeling career at the Central Aerological Observatory (CAO) in Russia.

Today, SAM is used by more than a dozen cloud modelers in the US and in Canada. A partial list of publications of the scientific results obtained using SAM can be found at the end of this page.

Model Highlights

Anelastic dynamical core;
Prognostic liquid/ice water static energy, total non-precipitating (cloud water/ice) and total precipitating water(rain/snow/graupel);
Diagnostic cloud water, cloud ice, rain, snow, and graupel;
1.5-order sub-grid scale closure (prognostic SGS TKE) or Smagorinsky-type closure;
Radiation from CCM3, CAM3, or CSU BUGS;
Periodical domain with the option of solid lateral walls (for beta-plane runs);
Surface fluxes based on Monin-Obukhov similarity;
ISCCP cloud simulator;
CAM3 physical parameterizations as an option for low-resolution runs;
Simple mixed-layer ocean;
Parallel (MPI).

Examples

Idealized GATE Simulation of Convection over Tropical Atlantic (“GigaLES”)

- Based on average forcing and sounding from GATE Phase III observations (30 August – 19 September 1074, Tropical Atlantic);
- Forcing: SST, horizontal advective tendencies of s and q; mean wind nudged to observed; radiative heating prescribed; surface fluxes – interactive.
- Domain: 2048x2048x256 grid points, or 205x205x27 km3 (horizontal grid spacing 100m);
- Vertical grid spacing: 50m below 1km, 50-100m @1-5km; 100m @5-18km; 100-300m above;
- Time step: 2 sec, duration: 1 day;
- Initialization: random small-amplitude noise in temperature near the surface;
- run done over 6 days wall-clock time on 2048 processors of IBM BlueGene BG/L of NYCCS;
- Animations of mock-up cloud albedo as would be seen from a satellite orbit (15 simulated minutes per movie second);
- One day evolution whole domain, Zoom-in into a quarter of a domain (100×100 km2) for 13.5 hours and Zoom-in into a 50×50 km2 subdomain for 2h40m:

Snapshot of a cloud scene at full model resolution (180×180 km2)

KWAJEX Simulation

23 July – 15 September 1999: 52 days, Kwajalein Atoll, Marshall Islands.
Forcing: SST, horizontal advective tendencies of s and q; large-scale vertical velocity; mean wind nudged to observed.
Radiation and surface fluxes – interactive.
Domain: 256x256x64 grid points, or 256x256x27 km3, time step: 10 sec, duration: 52 days
Snapshots of various cloud regimes:

KWAJEX Squalls

Squalls as viewed from above. Simulated satellite view of the cloud field produced by the SAM model.

KWAJEX Cumuli

Shallow ‘fair weather’ clouds as viewed from above. Simulated satellite view of the cloud field produced by the SAM model.

KWAJEX Congestus Clouds

Congestus clouds as viewed from above. Simulated satellite view of the cloud field produced by the SAM model.

KWAJEX Cumulonimbus

Cumulonimbus clouds as viewed from above. Simulated satellite view of the cloud field produced by the SAM model.

KWAJEX Cirrus Clouds

Cirrus clouds as viewed from above. Simulated satellite view of the cloud field produced by the SAM model.

TRMM-LBA High-Resolution Simulation

- - Based on TRMM-LBA Case 3 of the GCSS WG4;
  - Domain: 1536 x 1536 x 256 grid points, or 154 x 154 x 25 km3
  - Horizontal resolution: 100 m, vertical resolution: 50 m in PBL, 100 m in troposphere, 150-200 m in stratosphere
  - Time step: 2 sec; duration 6 hours.
  - Forcing: Prescribed surface fluxes and radiative cooling.
  - Case description: Starts early morning when no clouds present. About 2 hours into simulation, shallow convection develops gradually growing into mid-level convection with the transition to deep convection by the simulation end.
  - Snapshot of the cloud field at the end of simulation: pdf (1.5 Mb), jpg (80 kb). Note that the clouds tops are as high as 12 km.
  - Snapshot of a view from a satellite: pdf (620 kb), jpg (104 kb), and zoom into one quarter of the domain: pdf (540 kb), jpg (96 kb).
  - Zooming-in into the shallow cloud field: full (7.3 Mb), small (2.3 Mb). Note that even at the maximum zoom there is still plenty of resolution left.
  - Rotating cloud field at the end of simulation: full (35 Mb), small (10.4 Mb)

Download

More details and download link can be found here