Talk by David Noon – Niels Bohr Institute - University of Copenhagen

Talk by David Noon

Department of Atmospheric and Oceanic Sciences, University of Colorado, and
Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA

Factors controlling the water budget of the atmosphere using process models and contemporary observations of stable isotope ratios

Water plays a critical role in the climate system. On land water availability controls ecosystem production, in polar regions the changing ice sheets are composed of water which holds information about past climate, and water in the atmosphere dominates variability in the radiative properties of Earth. While much is known about the interwoven hydrological cycles on earth, there remains significant uncertainty about the processes which control the movement of water and their role in the regional and global climate. The stable isotope ratios of oxygen and hydrogen in water provide insight to the transport pathways because the natural fractionation of heavy 18O and 2H during phase change and because of diffusion. Isotope ratios are a gold standard for understanding past climate from proxy records. Satellite and in situ measurement technologies now allow isotope ratios to be paired with appropriate process models, including state-of-the-art climate models used in international assessments. We examine the humidity budget in the subtropics which is critical for understanding climate sensitivity. Measurements of stable isotope ratios in cloud particles water vapor and precipitation are used to determine the balances between contributions from large-scale transport, turbulence and cloud microphysical processes. We discuss both the importance of these constraints in providing insight beyond that available from traditional methods and some of the limitations associated with using stable isotope tracers in assessing atmospheric water cycles.