Unifying Atmospheric Composition in the Unified Forecasting System Through UFS-Chem Development

NOAA’s Unified Forecasting System (UFS) is a community-based Earth modeling system that plans to provide a framework to efficiently incorporate research advances into NOAA’s operational forecasts. Currently, chemistry related code for different applications including weather, climate, air quality, and smoke and dust forecasting is incorporated into the UFS through different methods. This non-unified framework is inefficient, difficult for developers to maintain, and not conducive for adding capabilities within the UFS for research applications. Through this work, we plan to unify atmospheric chemistry and composition within the UFS by creating CATChem or the Configurable ATmospheric Chemistry module (https://catchem.readthedocs.io/). CATChem will be flexible such that users can select the correct level of chemical complexity for their research or operational application. CATChem will include the following processes: passive tracers, chemical kinetics, aerosols, photolysis, wet deposition, dry deposition, connections to emissions, and connection to physics schemes. We will link CATChem to the UFS to create UFS-Chem or the Unified Forecasting System with chemistry. When possible, we will use tools already developed or being developed by the research community like the Model Independent Chemistry Module (MICM), which is a component of the MUlti-Scale Infrastructure for Chemistry and Aerosols (MUSICA), led by NCAR.

We will also add enhanced research capabilities into UFS-Chem, which will include: 

• Options to use gas and aerosol chemical mechanisms of varying complexity.
• Options for passive tracers, i.e. long lived greenhouse gases, which will also allow benchmark verification of mass conservation across UFS-Chem.
• Ability to easily couple different mechanisms to different physics options. 
• Development of a more flexible emissions processing system.
• Interfacing with state-of-science atmospheric composition data assimilation capabilities. 
• Further investment of model evaluation tools like MELODIES-MONET (https://melodies-monet.readthedocs.io) that efficiently compare model results against a variety of observations.

UFS-Chem will increase efficiency in code development, reduce costs for code maintenance, reduce time and effort for transitions to operations, and enhance collaborations with the research community. Continued engagement with the atmospheric chemistry and carbon cycle research communities are critical to ensure that research advances are efficiently and promptly included within the UFS, so that NOAA continues to provide state-of-the-art forecasts and monitoring of atmospheric composition to inform key societal challenges and policy. Here we present plans for UFS-Chem development and results for the first version of the global UFS configuration that includes full gas-phase tropospheric and stratospheric chemistry, which has been made possible through CATChem development.