The Common Community Physics Package (CCPP) is a library of physical parameterizations distributed with a framework that enables its use in any host model that incorporates CCPP into their own structure. CCPP is currently used with NOAA’s Unified Forecast System (UFS) for experimental subseasonal-to-seasonal, medium- and short-range weather, air quality, and hurricane applications, with all physics development for the UFS transitioned to CCPP. The CCPP framework was originally developed by DTC, and is now being co-developed by DTC and NCAR. Both NCAR and the Naval Research Laboratory are adopting CCPP for use in their models. The DTC also distributes the CCPP Single Column Model (SCM), which allows physics experimentation with the CCPP in a simplified setting. The capabilities inherent in the CCPP and its SCM form an optimal collaborative infrastructure for use in a simple-to-more-complex Hierarchical System Development (HSD) approach to test and improve modeling systems, where such an approach can more easily identify systematic biases in models.
The CCPP’s interoperability, specifically, its ability to be used by a wide variety of host models, derives from the method used to communicate variables between the physics and the host models. All variables required by a physical parameterization must be accompanied by metadata, including their standard name, units, rank, etc. Similarly, to be CCPP-compliant, the host models must include metadata about their variables. The CCPP framework compares the variables in the physics against those in the host and automatically generates physics caps, which are software interfaces for communicating variables.
The clearly defined software interfaces for communicating variables facilitate the use and development of the CCPP by the general community, while the interoperability aspects open the door for scientists at multiple organizations using diverse models to share code and work together on physics innovations. Desirable capabilities, such as scheme reordering in a physics suite, grouping schemes (calling one or more parameterizations from different parts of the host model), and subcycling (calling selected schemes at shorter time increments) make the CCPP framework suitable for use in research and operations, streamlining the R2O transition.
The physical parameterizations in the CCPP are typically used as sets by the host models, known as physics suites, and described using Suite Definition Files (SDFs). The CCPP framework permits a multi-suite build, in which multiple SDFs are selected at compile time and are available for use at runtime. This capability is appealing to both researchers and operational centers, since it enables flexibility, while maintaining high computational performance.
The CCPP is in a state of active development. Parameterizations are continuously improved and new schemes and suites are being added to meet the needs of various projects. Collaborative development is stimulated through the use of open-source code accessible via GitHub. Public releases of the CCPP with its SCM can be found at http://dtcenter.org/ccpp and the public release of the UFS Medium-Range Weather Application using CCPP is described at https://github.com/ufs-community/ufs-mrweather-app/wiki.
