Evaluation of WRF-VPRM CO2 Dynamical Downscaling over the Contiguous United States Using the ACT-America Data

Sources and sinks of CO₂ at regional scales remain poorly understood. Part of the difficulty is our limited knowledge regarding the impacts of synoptic-scale weather (particularly cyclones at mid-latitudes) on terrestrial CO₂ emission and atmospheric transport of CO₂. About 10 years ago, the Vegetation Photosynthesis and Respiration Model (VPRM) was coupled into the Weather Research and Forecasting (WRF) model to simulate "weather aware" biospheric CO₂ fluxes and subsequent transport. Such an online-coupling system (referred to as WRF-VPRM) can facilitate investigation of the impacts of weather on CO_2. Ten years have passed, however, WRF-VPRM was barely evaluated over the contiguous United States. The Atmospheric Carbon and Transport-America (ACT-America) mission obtained comprehensive airborne and ground-based measurements of CO₂ and meteorological variables over the eastern United States, providing an excellent dataset for evaluation of WRF-VPRM. In this study, atmospheric CO₂ concentrations from the Carbon Tracker global simulations are used as initial and boundary conditions for WRF-VPRM simulations with a resolution of 12 km over the contiguous United States for year 2016 and the downscaled CO₂ is evaluated using the ACT-America measurements. Initial results show that WRF-VPRM reasonably simulates the diurnal and seasonal variation of CO₂ fluxes and concentrations. The downscaling also successfully captures the passages of mid-latitude cyclones and shows interesting contrast of CO₂ across fronts. Analysis of these WRF-VPRM downscaling results could help examine the sources and sinks of CO₂ over the contiguous United States.