Figure 1.

Time evolution of XCO₂ from satellites and model. Latitude-time distribution of XCO₂ (in ppm) measured from OCO-2 (a) and GOSAT (e), and their differences with 3 cases of ACTM simulations (b–d and f–h, respectively) for the period of OCO-2 operation, from 07 September 2014 to 31 October 2016 (GOSAT ACOS b7.3 are available until 31 May 2016). Note the striking similarities between OCO-2 and GOSAT measurements and ACTM_IAV84 + GFAS simulation case, particularly over the tropics. Further detailed comparisons of GOSAT and ACTM, with separation for soundings over land and water surfaces suggests the positive model biases in the high latitude regions arise mainly over the ocean surface. Similar plots cannot be made using data from the TCCON or NOAA network sites without significant interpolation in space and time due to the geographically sparse sampling of the ground-based networks.