Water vapor transport and stable water isotopes

Water sources for heavy precipitation events (Andreas Winschall)

Tagging of moisture as a numerical tracer in a numerical weather prediction model allows tracking of water from the evaporation via phase changes and transport to precipitation and thus gives insight in the atmospheric water cycle. The particular focus is to use this tagging technique to determine the sources of water for heavy precipitation events. The figure shows a 3-dimensional picture of the isosurface of tagged water vapour evaporated from the Mediterranean (red) and from an Atlantic area of high evaporation (blue) both contributing to an Alpine heavy precipitation event in November 2002.

Measurements of stable water isotopes (Franziska Aemisegger)

Short term measurement series of the stable water isotope composition of vapour and precipitation can contribute to enhancing our process-based understanding of the spatio-temporal variability of the isotope signal in the atmospheric branch of the water cycle. Advanced knowledge about this variable can in turn give some hints on important moist atmospheric mechanisms like cloud formation, evaporation and evapotranspiration at the land surface. Measurements of stable water isotopes with a high (subhourly) temporal resolution will be performed in water vapour and precipitation in a prealpine catchment, close to an operational and extensive hydrometeorological measurement site in the IAC research catchment Rietholzbach in Switzerland. The data will be interpreted using Lagrangian and Eulerian model approaches that have been developed in our group. The figure shows the specific humidity following 3D kinematic backward trajectories from Zurich for the 21.03 2010 2300 UTC.

Stable water isotopes as tracers (Stephan Pfahl)

Stable water isotope ratios in natural waters are widely applied for analyzing the hydrological cycle and as proxies for past climate variations. We explore their suitability for serving as diagnostic tracers of atmospheric processes, focusing on short, synoptic time scales and specific weather events. Several model approaches are used for obtaining a better understanding of short-term variations in isotope signals, ranging from Lagrangian diagnostics to regional numerical weather forecast models. The figure shows an example of simulated deuterium excess in near surface water vapor over the Mediterranean from two of these modeling techniques (a: COSMO model simulation, b: diagnostic trajectory approach).

Lagrangian moisture source diagnostics (Harald Sodemann)

We have developed a method which allows to trace water vapour in the atmosphere backward in time to identify the location from which it has evaporated. The method is a diagnostic based on backward trajectories, and provides quantitative information on the various contributions from moisture sources to the water vapour in traced air parcels. This provides, for example, a physical link between anomalous sea surface temperatures and extreme precipitation events.

In combination with the Eulerian moisture source tagging, insight on key physical climate processes can be investigated. Various geographical regions are of interest, such as Antarctica and Greenland to understand paleo records of climate from ice cores, mid-latitudes to investigate the ingredients of precipitation extremes, and tropical region to understand e.g. Monsoon processes.