Canopy App: Models complex in-canopy effects in UFS based weather and atmospheric composition applications
Like most regional/global models, in the NOAA Unified Forecast System (UFS) weather and atmospheric composition modeling suite, the vegetation canopies are still treated as a 2-D surface (i.e., “big-leaf” approach) and only affect the atmosphere via boundary fluxes (e.g., emission and deposition). However, the dynamical and chemical environment within the in-canopy airspace is quite different, and can be generally characterized as having less light, reduced vertical mixing, and other differences compared to the atmosphere above. Considering the challenge of incorporating complex, explicit multi-layer canopy models into UFS, we introduce the development of Canopy-App (name inspired by those given to UFS modeling configurations; https://github.com/noaa-oar-arl/canopy-app), which is an effort to represent such complex in-canopy effects in regional-to-global weather and atmospheric composition applications under the UFS, building on established canopy parameterizations. Canopy-App is not intended as a complete 1-D canopy model. Rather, it uses relatively simple plant shape distribution functions for different vegetation types and computes select variables and adjustment factors used for efficiently modulating atmospheric quantities (such as gas-phase chemical species) due to vertically resolved canopy effects. These currently include: canopy-resolved biogenic emissions, photolysis attenuation; vertical turbulent diffusivity; and an in-canopy winds and wind adjustment factor (WAF) for fire spread and potentially other applications. With Canopy-App’s modular design, you can choose which to compute. While our preliminary work includes relatively simplified parameterizations, including a bulk photolysis attenuation factor treatment, we are working to advance Canopy-App processes. This includes reaction-dependent photolysis attenuation factors based on spectrally resolved canopy radiative transfer. Currently, Canopy-App runs standalone, but we also plan to integrate Canopy-App into the UFS via the Common Community Physics Packages (CCPP) and/or coupling as a model component under the Earth System Model Framework (ESMF). Ideally, the latter would allow Canopy-App to run both offline/stand-alone and online-coupled with different modeling systems under the ESMF.