Guillaume Tremoy & Olivier Cattani

FRANCE — In June, 2010 the LSCE installed a Picarro isotopic water Cavity Ring-Down Spectroscopy system that measures the isotopic composition of water vapor continuously  in Niamey (Niger) on the campus of the Institute of Radioisotopes (IRI). This facility collects rainwater and makes other isotope measurements. The Picarro instrument is being used for the continuous measurement of the isotopic composition of water vapor throughout the monsoon season. This data should help us better understand and quantify the physical processes that occur within convective systems (re-evaporation in the unsaturated column, recycling water surface).

By extension, with this knowledge we should be able to evaluate the convective parameterization in climate models that include factoring for water isotopes as part of climate calculations. The data should also give us evidence on the genesis and internal mechanisms of the monsoon in the context of regional atmospheric circulation. Lastly, a better understanding of the coupling between isotopic measurements in rain and vapor should allow us to refine our understanding of isotopic fractionations under tropical conditions and to better interpret the paleoclimatic records in terms of tropical climate variable quantified.

Until now, the lack of a technique for measuring in situ isotopic composition of water vapor had made it difficult to obtain such data and only a few scattered data sets existed. The Picarro instrument allows for continuous in situ vapor measurements and thus will provide the key tool to help us obtain more comprehensive data on isotopic water vapor. The contribution of these data both on the physics of isotopes, the understanding of tropical convection and paleoclimatology should be unique.