Index Geophysics

Global CO2 fluxes estimated from GOSAT retrievals of total column CO2

We present one of the first estimates of the global distribution of CO₂ surface fluxes using total column CO₂ measurements retrieved by the SRON-KIT RemoTeC algorithm from the Greenhouse gases Observing SATellite (GOSAT). We derive optimized fluxes from June 2009 to December 2010. We estimate fluxes from surface CO₂ measurements to use as baselines for comparing GOSAT data-derived fluxes. Assimilating only GOSAT data, we can reproduce the observed CO₂ time series at surface and TCCON sites in the tropics and the northern extra-tropics. In contrast, in the southern extra-tropics GOSAT X_CO₂ leads to enhanced seasonal cycle amplitudes compared to independent measurements, and we identify it as the result of a land–sea bias in our GOSAT X_CO₂ retrievals. A bias correction in the form of a global offset between GOSAT land and sea pixels in a joint inversion of satellite and surface measurements of CO₂ yields plausible global flux estimates which are more tightly constrained than in an inversion using surface CO₂ data alone. We show that assimilating the bias-corrected GOSAT data on top of surface CO₂ data (a) reduces the estimated global land sink of CO₂, and (b) shifts the terrestrial net uptake of carbon from the tropics to the extra-tropics. It is concluded that while GOSAT total column CO₂ provide useful constraints for source–sink inversions, small spatiotemporal biases – beyond what can be detected using current validation techniques – have serious consequences for optimized fluxes, even aggregated over continental scales.

Basu, S.

Guerlet, S.

Butz, A.

Houweling, S.

Hasekamp, O.

Aben, I.

Krummel, P.

Steele, P.

Langenfelds, R.

Torn, M.

Biraud, S.

Stephens, B.

Andrews, A.

Worthy, D.

2018-01-15

Text

application/pdf

10.5194/acp-13-8695-2013

https://acp.copernicus.org/articles/13/8695/2013/

eISSN: 1680-7324

eng