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Stochastic Physics - Earth Prediction Innovation Center
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Stochastic Physics

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Welcome

The Unified Forecast System (UFS) is a community-based, coupled, comprehensive Earth modeling system that includes multiple applications, models, and components. NOAA’s operational model suite for numerical weather prediction (NWP) is quickly transitioning to the UFS from a number of different modeling systems. The UFS enables research, development, and contribution opportunities within the broader Weather Enterprise (including government, industry, and academia). For more information about the UFS, visit the UFS Portal.

Description

Stochastic physics is a component of the UFS Weather Model (WM) and contains a variety of stochastic schemes. The schemes add valuable scientific and numerical impact by addressing dynamical effects of unresolved scales in the UFS WM forecast system. Stochastic Kinetic Energy Backscatter (SKEB; Berner et al., 2009), Stochastically Perturbed Physics Tendencies (SPPT; Palmer et al., 2009), and Specific Humidity perturbations (SHUM; inspired by Tompkins and Berner, 2008) are what is known as “ad-hoc” schemes; their perturbations are prescribed based on a white-noise perturbation field and added to parameter tendencies or state fields to achieve ensemble spread.

In addition, there are the capabilities to perturb certain land model/surface parameters (Gehne et al., 2019 and Draper 2021), and a cellular automata scheme (Bengtsson et al. 2013), which interacts directly with the convective parameterization. Stochastic Parameter Perturbation (SPP) represents a more targeted stochastics physics method, where parameters within physics schemes are directly perturbed based on a perturbation field that is coherent in time and space. SPP achieves adequate spread through the perturbation of many parameters across multiple physics schemes. The land model/surface parameter perturbations are essentially an implementation of SPP within the land-surface model physics parameterization. The cellular automata scheme applies a stochastically-perturbed organization of sub- and cross-grid convection within the cumulus scheme of a given model. More detailed information on these stochastic physics schemes can be found in the Stochastic Physics User’s Guide.

Getting Started

Stochastic physics currently only works within the UFS WM. Users can get the full system by downloading the UFS WM or UFS application code containing the WM (e.g., Short-Range Weather [SRW] Application code) and enabling stochastic physics via namelist options. For example, in the SRW App, users would need to add stochastic physics parameters to their configuration file (i.e., config.yaml). Users can also turn on the stochastic physics options in WM regression tests by adding lines to the test file that override the default stochastic physics options in default_vars.sh

Users specifically interested in the stochastic physics code can start by running the stochastic physics unit tests. However, the stochastic physics unit tests are only configured to run on Hera; users must be logged into that machine or have a good understanding of their system and bash scripting in order to configure the tests for their system. After cloning the stochastic_physics repository, navigate to the unit_tests directory and run the run_standalone.sh script, which will submit the unit tests to Slurm as a batch job: 

sbatch run_standalone.sh

The standalone_stochy.x executable will then be generated using GNU compilers, and when executed within the same shell script, six output data tiles are created in the newly generated stochy_out directory. Output tiles will be named workg_T82_504x248.tile0#.nc, where # refers to tiles numbered 1-6.

Documentation & User Support

Version

Description

Documentation for the head of the master branch. This may have gaps and errors.

Documentation for stochastic physics in the v2.x.x releases of the SRW App.

Users can also get expert help through the GitHub Discussions Q&A.









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