Simulation of d18O in precipitation by the regional circulation model REMOiso
Résumé
The first results of a regional circulation model REMOiso fitted with water isotope diagnostics are compared with various isotope series from central Europe. A 2 year case study is conducted from March 1997 to February 1999 centred over Europe, analysing daily and monthly measurements. Isotope signals over Europe are dominated by the typical isotopic effects such as temperature, continental and altitude effects, both on annual and seasonal scales. These well-known isotopic effects are successfully reproduced by REMOiso, using two different boundary data sets. In a first simulation, the European Centre for Medium-range Weather Forecasts (ECMWF) analyses serve as boundary conditions, where water isotopes were parameterized by a simple temperature dependence. In a second simulation, boundary conditions both for climatic and isotopic variables are taken from the ECHAMiso general circulation model output. The comparison of both simulations shows a very high sensitivity of the simulated ?18O signal to boundary conditions. The ECMWF-nested simulation shows an average offset of 4Ð5‰ in mean ?18O values and exaggerated seasonal amplitude. The ECHAM-nested simulation represents correctly the observed mean ?18O values, although with a dampened seasonality. REMOiso's isotope module is further validated against daily ?18O measurements at selected stations (Nordeney, Arkona and Hohenpeissenberg) situated in Germany.