Analysis of XCO2 retrievals for cloudy ocean measurements from GOSAT

Abstract

The atmospheric carbon dioxide (CO2) concentration has risen from 278 parts per million (ppm) in 1750 to 390.5 ppm in 2011. This increase is caused by anthropogenic emission, predominantly fossil fuel combustion. There is sufficient capacity in the oceans to take up to 70 to 80% of this amount, however, due to the large time scale of this process it can take several hundred years to reach this value. The response of these sinks to a changing climate are important to predict the future behaviour of the carbon cyclewith increasing emissions. Space-based observations of column averaged CO2 dry air mole fraction (XCO2) with near-global coverage can be used to better quantify the fluxes of small- scale sinks and sources. The current data set can be significantly extended by performing XCO2 retrievals for measurements above cloudy ocean scenes as proposed by [Schepers et al., 2016]. This method is based on a full physics retrieval algorithm called RemoTeC, which has been used to retrieve XCO2 and XCH4 from GOSAT land and glint measurements. In this study the cloudy retrieval method is performed on a larger scale and an analysis of the data yield and increased spatial coverage of XCO2 over the oceans is done, a quantitative comparison is made with GOSAT XCO2 retrievals obtained from TCCON, clear- sky land and glint ocean measurements and the influence of cloud climatology on the retrievals per- formance is assessed. The cloudy retrieval was done for GOSAT L1B spectra frommeasurements obtained between 2009 and 2013 for several areas of interest: North-America, South-America, East-Asia, Oceania and a strip of Pacific Ocean. After a priori filtering for clouds and other parameters, on average 14% of the retrievals gave successful results.