A View on Mid-Tropospheric CH4 and CO2 in the Tropics: 6 Years from MetOp-A/IASI
Crevoisier, Cyril¹; Armante, Raymond¹; Thonat, Thibaud¹; Massart, Sébastien²; Cressot, Cindy³; Crépeau, Laurent¹; Scott, Noelle¹; Chédin, Alain^1
1CNRS/LMD, FRANCE; ²ECMWF, UNITED KINGDOM; ³LSCE/IPSL, FRANCE

Since July 2007, monthly averages of mid-tropospheric methane and upper-tropospheric carbon dioxide are retrieved in the tropics over land and sea, by day and night, from IASI onboard MetOp-A, yielding a complete view of the geographical distribution, seasonality and long-term tendency of these gases in the mid-troposphere. Through comparisons with regular aircraft measurements of the CONTRAIL and CARIBIC programs, we will show that IASI captures well the evolution of mid-tropospheric methane with an averaged difference between collocated IASI estimates and CARIBIC measurements of 7.2 ppbv with a standard deviation of 13.1 ppbv for methane. We will show that IASI captures the trend and interannual variation of both greenhouse gases, with an excellent agreement with the rate of increase measured at the surface, giving confidence in the ability of IASI to follow their evolution over the 20 years of EPS/MetOp program. We will discuss the 6-year evolution of CH4 and CO2 in light of the recent evolution of surface emissions and climate conditions. Finally, we will discuss the use of IASI CH4 and CO2 fields to infer the space-time distribution of methane total column and surface emissions that is currently being investigated in the framework of the MACC-II/GMES initiative and the ESA Climate Change Initiative.