Séminaire

Water isotopologues are useful as tracers of hydrological processes in the atmosphere, and their presence in paleoclimate proxies gives us a window into past climates.  In the present climate, they offer hope for improving our understanding of moist processes and possibly improving moist physics parameterizations through the extra constraints they provide on the hydrological cycle. In this talk, we'll describe connections between deep convection over the tropical oceans and the isotopic composition of vapor and precipitation and suggest ways in which isotopes might be able to provide useful information about the present climate.

First, we will highlight the relationship between moisture convergence and the isotopic composition of precipitation.  Over the tropical oceans, the amount and isotopic composition of precipitation are inversely correlated.  This can be seen to arise from the moisture budget of the column, with regions of strong precipitation relying on the convergence of isotopically-depleted moisture rather than relatively more isotopically-enriched surface evaporation.  This viewpoint leads to connections between isotopic fields, the hydrological cycle and the large-scale circulation. This relationship between the moisture budget imbalance (or P-E) and isotopic composition can also be seen in mid-tropospheric water vapor across the phases of ENSO and suggest the potential of water vapor isotopic composition as a tracer for P-E. Further, as seen in the work of Torri, Ma and Kuang, the depth of moisture convergence into a convective region is itself related to the isotopic composition of precipitation, as water vapor is increasingly depleted in heavy isotopes through the troposphere. Here, the isotopic
composition of precipitation may be able to serve as an additional constraint on the vertical structure of ascent in convective regions.

Past studies have illustrated connections between water vapor isotopic composition across the cycle of the Madden-Julian Oscillation.  Here, we will introduce a new isotope-enable  global model, iSPCAM, the relies on superparameterization and exhibits variability at MJO time and length scales.  Initial results with the model will be presented, highlighting the structures of water vapor and its isotopic composition across a composite MJO event.

marie-pierre.lefebvre@lmd.jussieu.fr