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The Monitoring Atmospheric Composition and Climate Interim Implementation(MACC-II) delayed-mode (DM) system has been producing an atmospheric methane(CH4) analysis 6 months behind real time since June 2009. This analysisused to rely on the assimilation of the CH4 product from the SCanningImaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY)instrument onboard Envisat. Recently the Laboratoire deMétéorologie Dynamique (LMD) CH4 products from the InfraredAtmospheric Sounding Interferometer (IASI) and the SRON Netherlands Institutefor Space Research CH4 products from the Thermal And Near-infrared Sensorfor carbon Observation (TANSO) were added to the DM system. With the loss ofEnvisat in April 2012, the DM system now has to rely on the assimilation ofmethane data from TANSO and IASI. This paper documents the impact of thischange in the observing system on the methane tropospheric analysis. It isbased on four experiments: one free run and three analyses from respectivelythe assimilation of SCIAMACHY, TANSO and a combination of TANSO and IASICH4 products in the MACC-II system. The period between December 2010 andApril 2012 is studied. The SCIAMACHY experiment globally underestimates thetropospheric methane by 35 part per billion (ppb) compared to the HIAPERPole-to-Pole Observations (HIPPO) data and by 28 ppb compared the TotalCarbon Column Observing Network (TCCON) data, while the free run presents anunderestimation of 5 ppb and 1 ppb against the same HIPPO andTCCON data, respectively. The assimilated TANSO product changed in October2011 from version v.1 to version v.2.0. The analysis of version v.1 globallyunderestimates the tropospheric methane by 18 ppb compared to theHIPPO data and by 15 ppb compared to the TCCON data. In contrast, theanalysis of version v.2.0 globally overestimates the column by 3 ppb.When the high density IASI data are added in the tropical region between30° N and 30° S, their impact is mainly positive but morepronounced and effective when combined with version v.2.0 of the TANSOproducts. The resulting analysis globally underestimates the column-averageddry-air mole fractions of methane (xCH4) just under 1 ppb onaverage compared to the TCCON data, whereas in the tropics it overestimatesxCH4 by about 3 ppb. The random error is estimated to be lessthan 7 ppb when compared to TCCON data

Assimilation of atmospheric methane products into the MACC-II system: from SCIAMACHY to TANSO and IASI