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TitleEnsemble model output of North American atmospheric CO2 simulations for summer 2016, including transport, CASA and CT2017, and boundary condition ensembles
Date2020
AbstractTerrestrial biosphere models (TBMs) play a key role in detection and attribution of carbon cycle processes at local to global scales, and in projections of the coupled carbon-climate system. TBM evaluation commonly involves direct comparison to fluxes estimated from eddy covariance measurements. This study uses atmospheric CO2 mole fraction ([CO2]) measured in situ from aircraft and tower, in addition to flux tower data, during summer 2016 to evaluate the CASA TBM and infer process error. WRF-Chem is used to simulate [CO2] using a variety of biogenic CO2 fluxes from the CASA parameter-based ensemble and CarbonTracker version 2017 (CT2017) in addition to transport and CO2 boundary condition ensembles. The resulting “super ensemble” of modeled [CO2] demonstrates that the biosphere introduces the majority of uncertainty to the simulations and that biogenic [CO2] can be lifted by the fronts beyond the top of atmospheric boundary layer. Both aircraft and tower [CO2] data consistently show that the CASA ensemble net ecosystem exchange (NEE) of CO2 is biased high (NEE too positive) and identify that the maximum light use efficiency Emax is the key parameter that drives the spread of the current CASA ensemble. These findings are verified with flux tower data. The direct comparison of the CASA flux ensemble with eddy covariance flux measurements from the AmeriFlux network indicates the modeled [CO2] biases are mainly due to missing sink processes in CASA. Separating the daytime and nighttime flux, we discover that the underestimated net uptake results from missing sink processes that result in overestimation of respiration. Such biases are smaller in the CT2017 biogenic flux product, which assimilates observed [CO2], however, further analyses reveal unrealistic overestimation of nighttime respiration in CT2017. This ensemble model output includes 10 WRF-Chem CO2 transport simulations. Each transport simulation comprises 29 CO2 biogenic fluxes, and five boundary conditions from various global models. WRF-Chem transport simulation at 27 km x 27 km with 51 vertical levels for the time period of 2010. Detailed description of model setup and associated results can be found in Feng et al, [2019a, 2019b].
MetadataClick here for full metadata
Data DOIdoi:10.26208/z864-qk73

Researchers
Feng, S.
Penn State Department of Meteorology
Lauvaux, T.
Penn State Department of Meteorology
Williams, C.
Clark University
Davis, K. J.
Penn State Department of Meteorology
Zhou, Y.
Clark University
Baker, I.
Colorado State University, Fort Collins, USA
Barkley, Z. R.
Penn State Department of Meteorology
Wesloh, D.
Penn State Department of Meteorology

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References
S. Feng, T. Lauvuax, K. Klaus, K. Davis, P. Rayner, T. Oda, K. Gurney, 2019a: A road map for improving the treatment of uncertainties in high-resolution regional carbon flux estimates. Geophys. Res. Lett., 46. https://doi.org/10.1029/2019GL082987
Feng, S., Lauvaux, T., Davis, K. J., Keller, K., Zhou, Y., Williams, C., et al. (2019b). Seasonal Characteristics of Model Uncertainties From Biogenic Fluxes, Transport, and Large-Scale Boundary Inflow in Atmospheric CO2 Simulations Over North America. Journal of Geophysical Research: Atmospheres, 124(24), 14325–14346. https://doi.org/10.1029/2019JD031165