Simulation and Observation of Global Atmospheric CO2 from 2009-2010

We compare global variations in atmospheric CO2 concentrations using a comprehensive model of surface carbon cycling and atmospheric transport to retrievals of column CO2 mole fraction from near-infrared spectroscopy from the GOSAT mission. Surface carbon exchanges due to photosynthesis, respiration, decomposition, biomass burning, fossil fuel combustion, and air-sea gas exchange are computed every hour. These fluxes are used as input to a global atmospheric tranport model to obtain three-dimensional fields of CO2, which are sampled at the time and location of quality-screened GOSAT data retrieved by the Atmospheric Carbon Observations from Space (ACOS) team. The system is operated on a 0.5° x 0.67° grid (dx ~ 50 km), providing global mesoscale coverage, and has good skill at replicating diurnal, synoptic, and seasonal variations over vegetated land surfaces. It is driven by meteorological output from the NASA Goddard EOS Data Assimilation System. Surface weather from the system drives calculations of terrestrial ecosystem metabolism (radiation, precipitation, humidity, temperature) and air-sea gas exchange (wind), with other input data coming from satellite data products. Simulated spatial patterns and seasonal variations of simulated and observed column CO2 exhibit broad agreement, but some offsets in latitude and seasonal variations are noted. These are attributed to both model and satellite retrieval errors.