HR: 1340h
AN: PP43B-1277    [Abstracts]
TI: Influence of Convective Processes on Isotopic Composition of Precipitation (Oxygen 18 and Deuterium) in the Tropics: a Single Column Model Analysis
AU: Bony, S
EM: bony@lmd.jussieu.fr
AF: Laboratoire de Meteorologie Dynamique, Case 99, 4, place Jussieu, Paris, 75005, France
AU: * Risi, C M
EM: crlmd@lmd.jussieu.fr
AF: Laboratoire de Meteorologie Dynamique, Case 99, 4, place Jussieu, Paris, 75005, France
AU: Vimeux, F
EM: vimeux@lsce.saclay.cea.fr
AF: IRD-UR Great Ice/IPSL-LSCE, CEA Saclay, Orme des Merisiers, Batiment 701, Gif-sur- Yvette, 91191, France
AB: Isotopic records (deuterium and oxygen 18) in ice cores are a valuable tools to reconstruct past climate. However, the climatic interpretation of tropical istotopic records is still debated. The amount effect, which is the observed link between precipitation amount and isotopic composition of precipitation, largely controls the isotopic composition of precipitation there. Yet physical processes underlying this effect are still poorly understood and quantified. This is partly because most of tropical precipitations are related to atmospheric convective processes, whose influence on isotopic composition of precipitation is not well known. In the present study, water stable isotopes (H₂O¹⁸ and HDO) have been introduced into the Emanuel convective parametrization, and into a single column model of radiative-convective equilibrium including the convective parametrization and a parametrization of clouds and radiation. The detailed representation of processes such as mixing and rain evaporation in the Emanuel parametrization allows an investigation of the influence of convective processes on isotopic composition of precipitation (both δ D and deuterium excess). In particular, the physical processes underlying the amount effect are analyzed and their relative contributions are quantified. We show that the amount effect is actually the net effect of a combination of different convective processes. Two processes are dominant: first, the reevaporation of the falling rain and the diffusive exchange with the surrounding vapor in unsaturated downdrafts; second, the recycling of the subcloud layer vapor feeding the convective system by the mass flux driven by the reevaporation of rain. This calls for a detailed representation in models of processes associated with the reevaporation of convective rain to accurately simulate the isotopic composition of precipitation in the Tropics. We also investigate the time scales involved in the relationship between convective activity and the isotopic composition of precipitation.
DE: 0365 Troposphere: composition and chemistry
DE: 3314 Convective processes
DE: 3374 Tropical meteorology
DE: 4870 Stable isotopes (0454, 1041)
DE: 4932 Ice cores (0724)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting