Atmospheric water cycle and Stable isotopes

Water vapour is the most important trace gas in the atmosphere. Its concentration varies strongly with time and space. Due to evaporative cooling and latent heat release it is a fundamental element of the energy turnover in the earth system. With its stable isotopologues composition quantitfied by deltaD, delta18O and the d-excess, water vapour contains natural tracers of the phase change history during its atmospheric lifetime.

We use and develop a range of model tools, and collect observations from a range of instrumentation. A primary model tool is a Lagrangian moisture source diagnostic, which we use to identify the evaporation sources, transport pathways and arrivial regions for precipitation. The method is based on particle trajectories calculated using reanalysis, analysis and forecast data from weather prediction and climate models. A second method is based on artificial tracers of water vapour in regional models. Implemented in a secondary hydrological cycle of the model, these tracers tag moisture with a certain origin, which allows to trace its pathway from source to sink. 

Both model approaches are combined with measurements of the stable isotope composition of water vapour. We use observations from rain and snow at high resolution, surface waters, as well as water vapour measured on land stations, ship and aircraft to create a coherent perspective of the isotopic signal in the atmospheric water cycle. Within the Norwegian national infrastructure FARLAB a range of state-of-the-art instrumentation is available to quantify the stable isotope composition with the required high precision to decipher the isotope imformation on meteorological time scales (minutes to days). International and national collaboration is an integratal element in conducting these activities, such as in the projects and campaigns HYMEX/KIT, ACE, AC-AHC2 and SNOWPACE.