Miller, John: NOAA Global Monitoring Laboratory (Project Lead)
Basu, Sourish: NASA GSFC GMAO / University of Maryland (Co-Investigator)
Project Funding:
2012 - 2014
NRA: 2011 NASA: Carbon Monitoring System
Funded by NASA
Abstract:
The fundamental objective of the NASA Carbon Monitoring System (CMS) flux product is to derive surface CO2 fluxes using satellite-based column CO2 mole fractions. Although the CMS flux product has an existing evaluation strategy, it is limited in scope and has acknowledged shortcomings, especially with regard to tropical carbon fluxes. Here, we propose to use the large number of high-accuracy, high-precision, globally distributed in situ tropospheric CO2 observations (including a unique set of tropical observations) to assess the realism of the optimized CMS fluxes and their stated uncertainties. First, CO2 observations will be compared directly with a posteriori CMS-modeled CO2 mole fractions. To first-order, near surface CO2 surpluses in the modeled CO2 mole fractions can be interpreted as excess positive surface flux, and vice versa. Second, CMS fluxes will be compared to fluxes derived from independent flux optimization systems (using in situ CO2 data). This more direct flux evaluation will be conducted globally using the CarbonTracker data assimilation system. Moreover, CarbonTracker will be run using multiple transport models to help assess the role of transport errors in the mismatch between simulation and observation. Additionally, in tropical South America we will use a state of the art regional flux inversion system to create a second set of fluxes, taking advantage of a two-year data set of fortnightly measurements in Brazil at four vertical profile sites and two additional surface sites. Tropical South America is of particular interest in global satellite-based inversions because of its disproportionate importance for the global carbon cycle combined with the anticipated seasonal biases in tropical satellite-based column CO2 arising from frequent cloud cover and high aerosol loadings. Working with the CMS flux product team, we will use the in situ CO2-based flux evaluations to diagnose shortcomings in the existing CMS flux optimization approach, transport parameterization and input GOSAT/ACOS CO2 columns. Finally, while we do expect OCO-2 to ultimately have better coverage than GOSAT over tropical South America, we still anticipate significant seasonal biases in sensitivity to Amazonian surface fluxes. To address this issue, and guard against biases in eventual CO2 flux optimization, we will produce an in situ CO2-optimized flux map for use as a prior in future CMS flux products. For any top-down CO2 flux estimation system, evaluation and uncertainty characterization is as important as the flux calculation itself, and the research proposed here will leverage the highest precision measurements in the global carbon cycle to assess the quality of the CMS flux product.
Publications:
Alden, C. B., Miller, J. B., Gatti, L. V., Gloor, M. M., Guan, K., Michalak, A. M., Laan-Luijkx, I. T., Touma, D., Andrews, A., Basso, L. S., Correia, C. S. C., Domingues, L. G., Joiner, J., Krol, M. C., Lyapustin, A. I., Peters, W., Shiga, Y. P., Thoning, K., Velde, I. R., Leeuwen, T. T., Yadav, V., Diffenbaugh, N. S. 2016. Regional atmospheric CO
2
inversion reveals seasonal and geographic differences in Amazon net biome exchange. Global Change Biology. 22(10), 3427-3443. DOI: 10.1111/gcb.13305
More details may be found in the following project profile(s):
