Observational evidence of 3-D cloud effects in OCO-2 CO2 retrievals

These decreases are consistent with an interpretative framework provided by 3-D SHDOM radiative transfer calculations. Two 3-D metrics,.XCO2 and Have, are calculated and applied..XCO2 is the difference in XCO2 for the smallest and largest radiance bins. Have is a measure of the heterogeneity of the cloud radiance field.

Lines of XCO2 and MODIS radiance for four target mode scenes have different slopes for clear and cloudy scenes, contrary to the radiance-level retrieval artifact interpretation. In contrast, the graph of.XCO2 and MODIS Have for the various scenes has a linear correlation coefficient of 0.92, consistent with the 3-D interpretation. Since the OCO-2 measurement requirement is 1 ppmv, the cloudy scene XCO2 standard deviations between 1.2 and 2.6 ppmv indicate that 3-D cloud effects add an important component to the XCO2 error budget.