New insights into the hydrological cycle from IASI δD distributions across theglobe

International audienceBecause they have different vapour pressures, the different isotopologues of water (H216O and HDO)preferentially evaporate or condense during phase changes, leading to a fractionation of their ratio(δD). Numerous key processes of the hydrological cycle - such as convection, re-evaporation ofhydrometeors, evapotranspiration, mixing - mark distinctly the isotopic ratio of the air masses.Observations of δD constitute therefore a useful constraint on the moistening/drying processes. IASIprovide observations of δD in the free troposphere, after inversion of the measured radiances, at anunprecedented resolution.In this presentation, we illustrate the IASI capabilities to retrieve δD in the troposphere and show firstdistributions across the globe. The interest of these distributions is presented by analyzing theinformation contained in δD. For example, we show that the height of convection gives the watervapour a particular isotopic fingerprint which is of great interest to evaluate the representation oftropospheric mixing in climate models. We also present long term (6 years) time-series in the NorthernAtlantic. The seasonal and inter-annual variations are interpreted with backward trajectory analysesand we show that the Saharan dynamic strongly influence the isotopic composition above the AtlanticOcean through the formation of the Saharan Heat Low