GOSAT Retrievals Of CH4 And CO2 And Their Comparisons To Global Chemistry Transport Models

Global observations of total column CH4 and CO2 from space-based shortwave infrared measurements are well suited to improve our knowledge of the underlying surface fluxes. However, inferring these surface fluxes from total column data requires stringent levels of measurement precision and accuracy, representing a major challenge for the trace gas retrieval algorithms mainly due to spectral interference from atmospheric aerosols and clouds. This paper presents global retrievals of CH4 and CO2 columns from the shortwave infrared bands of the GOSAT satellite for the years 2009 to 2012. The retrieved CH4 and CO2 columns have now reached a high level of accuracy and precisions (0.7% for XCH4 and 0.6% for XCO2) as is demonstrated from the validation of the retrieved CH4 and CO2 columns against observations from Total Carbon Column Observing Network (TCCON). Global transport models are used to calculate the atmospheric concentrations of CH4 and CO2 based on a combination of emission inventories and biospheric fluxes from land surface models or alternatively on optimized surface fluxes obtained by assimilating in-situ observations from the surface networks. We have used the CH4 and CO2 columns from GOSAT to challenge model calculations from several state of the art global transport models and to diagnose the capability of the models to reproduce the regional spatio-temporal distributions of CO2 and CH4 as observed by GOSAT.