An evaluation of observed and simulated high-resolution records of stable isotopes in precipitation

• Main Author: Barras, Vaughan J. I.
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of Melbourne 2007
• Subjects: Rain and rainfall > Australia > Victoria; Rain and rainfall > Australia > Tasmania; Isotopes; Water vapor; Atmospheric; Clouds; Lagrangian functions; Southern Ocean
• Online Access: http://hdl.handle.net/11343/342574

Typescript Thesis (PhD) -- University of Melbourne, Faculty of Science, 2007 Includes bibliographical references (leaves 249-268) The relative abundances of the stable isotopes 180 and 2H in precipitation act as natural archives of information about local moisture history. As such, they are an important resource and a valuable interpretative tool in hydrological studies. In order to fully appreciate the climatological signal preserved in natural records, isotopic variability must be understood at the synoptic timescale. This has been investigated here through detailed observational analyses and model simulation over a range of timescales. Isotope records collected at two locations in Tasmania, Australia showed a relationship between rainfall amount and the extent of isotope depletion. Semi-Lagrangian trajectory analyses of individual events from these records indicate that there is a limited remote forcing upon local isotopic variability, with the majority of low level moisture entrainment occurring over the 24-48 hour period prior to arrival. The Southern Ocean was identified as the primary origin for low level air masses associated with rainfall over both southeastern and northwestern Tasmania, with some air masses highly depleted in 180 originating in the Tasman Sea influencing the eastern coast in summer. To further investigate the effect of local isotope modification, the Melbourne University Network of Isotopes in Precipitation (MUNIP) was established to examine the use of isotopes as a diagnostic of moisture history and atmospheric dynamics over as highly resolved a scale in both time and space as possible. From three separate observational campaigns of rain events across Melbourne, Australia, the structure of frontal cloud bands and pulse convective thunderstorms were successfully detected by isotopic measurements from sampled rainfall. The MUNIP results were used as a basis to test the performance of simulations of the three events by a version of the NCAR-CAM3 model with isotope hydrology. The ...