Assessing temporal clear-sky errors in assimilation of satellite CO2 retrievals using a global transport model
- Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado, USA
Abstract. The Orbiting Carbon Observatory (OCO) and the Greenhouse gases Observing SATellite (GOSAT) will make global observations of the total column dry-air mole fraction of atmospheric CO2 (XCO2) starting in 2008. Although satellites have global coverage, XCO2 retrievals will be made only a few times each month over a given location and will only be sampled in clear conditions. Modelers will use XCO2 in atmospheric inversions to estimate carbon sources and sinks; however, if satellite measurements are used to represent temporal averages, modelers may incur temporal sampling errors. We investigate these errors using a global transport model. Temporal sampling errors vary with time and location, exhibit spatially coherent patterns, and are greatest over land and during summer. These errors often exceed 1 ppm and must be addressed in a data assimilation system by correct simulation of synoptic CO2 variations associated with cloud systems.