F. Aemisegger

Isotope meteorology of cold front passages: A case study combining observations and modeling

This study investigates the role of below-cloud evaporation and evapotranspiration for the short-term variability of stable isotopes in near-surface water vapor and precipitation associated with central European cold fronts. To this end, a combination of observations with high temporal resolution and numerical sensitivity experiments with the isotope-enabled regional weather prediction model COSMOiso is used. The representation of the interaction between rain droplets and ambient vapor below the cloud is fundamental for adequately simulating precipitation isotopes ((p)) and total rainfall amount. Neglecting these effects leads to depletion biases of 20-40 in delta H-2(p) and 5-10% in delta O-18(p) and to an increase of 74% in rainfall amount. Isotope fractionation during soil evaporation is of primary importance for correctly simulating the variability of continental low-level vapor delta H-2(v) and delta O-18(v) and particularly of the secondary isotope parameter deuterium excess (d(v)). (Less)

The Climatological Impacts of Continental Surface Evaporation, Rainout, and Subcloud Processes on δD of Water Vapor and Precipitation in Europe

All types of applications of stable water isotopes, e.g. for the reconstruction of paleotemperatures or for climate model validation, rely on a proper understanding of the mechanisms determining the isotopic composition of water vapor and precipitation. In this study, we use the isotope-enabled limited-area model COSMOiso to characterize the impacts of continental evapotranspiration, rainout, and subcloud processes on δD of European water vapor and precipitation. To this end, we first confirm a reliable implementation of the most important isotope fractionation processes in COSMOiso by comparing 5 years of modeled δD values with multi-platform δD observations from Europe (remote sensing observations of the δD of water vapor around 2.6 km a.g.l., in situ δD measurements in near-surface water vapor, and δD precipitation data from the Global Network of Isotopes in Precipitation). Based on six 15 year sensitivity simulations, we then quantify the climatological impacts of the different fractionation processes on the δD values. We find δD of European water vapor and precipitation to be most strongly controlled by rainout. Superimposed to this are the effect of subcloud processes, which especially affects δD in precipitation under warm conditions, and the effect of continental evapotranspiration, which exerts an important control over the δD of near-surface water vapor. In future studies, the validated COSMOiso model can be employed in a similar way for a comprehensive interpretation of European isotope records from climatologically different time periods.

A Climatology of Strong Large-Scale Ocean Evaporation Events. Part II: Relevance for the Deuterium Excess Signature of the Evaporation Flux

AbstractThis paper discusses the relevance of transient events of strong large-scale ocean evaporation (SLOE) for the deuterium excess of marine boundary layer vapor d using a theoretical framework...