HR: 12:05h
AN: B12C-08 INVITED    [Abstracts]
TI: Global scale water isotope observations and the impact of the terrestrial biosphere on atmospheric hydrology
AU: * Noone, D `
EM: dcn@colorado.edu
AF: Department of Atmospheric and Oceanic Sciences, University of Colorado, CIRES Cambus Box 216, Boulder, CO 80309-0216, United States
AU: Brown, D
EM: Derek.Brown@colorado.edu
AF: Department of Atmospheric and Oceanic Sciences, University of Colorado, CIRES Cambus Box 216, Boulder, CO 80309-0216, United States
AU: Worden, J
EM: John.Worden@jpl.nasa.gov
AF: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, United States
AB: Water isotope measurements are known to be extremely useful for identifying hydrologic exchange processes at both single site scales and at larger scales from networks of, for instance, precipitation. Recent advances in observational techniques have allowed the development of a global scale dataset of the HDO to H₂O isotope ratio in lower troposphere from spacecraft. The HDO estimates are found though a spectroscopic retrieval based on high resolution and well calibrated infrared spectra obtained from the Tropospheric Emission Spectrometer (TES) on NASA's Aura spacecraft. With these global scale observations available almost every two days, the ability to use isotopes to understand the impact of the terrestrial biosphere on atmospheric hydrology has become a possibility at not just local scales but for large geographic regions. Simulating the isotope exchange in global climate models continues to advance, but now such models can for the first time be validated and tested with observations. Further, with models, the importance of the processes identified in the observational data can be assessed in detail. Of particular interest is identifying the terrestrial source of atmospheric water vapor, and specifically continental evapotransipration. Using a combination of the satellite observations and model simulations, we identify the terrestrial source of atmospheric water, and demonstrate its importance is larger than previously recognized. This can be deduced from the observations since the isotopic signature of transpired water reflects the isotopic composition of precipitation, while that of oceanic origin reflects the disequilibrium fractionation during evaporation from the ocean. Based on these results and guided by model simulations, we speculate that should the land use characteristics of the tropical continental regions change, and reflect more arid environments, the impacts on the atmospheric hydrology and climate is more than of just local in extent. The use of the deuterium excess parameter allows continental exchange to be partitioned between evaporation from soil and standing water, and transpiration, and therefore a highly desirable quantity to measure. While the capacity to observe the ¹⁸O isotope in H₂O from the TES exists, the signal to noise ratio in the data make estimation difficult for single atmospheric profiles. Nonetheless, mean statistics show promise. We describe the issues in the measurement technique that makes estimation of ¹⁸O challenging, and outline what requirements a next generation instruments should meet were it to specifically target understanding hydrologic processes with water isotope observations.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0365 Troposphere: composition and chemistry
DE: 0416 Biogeophysics
DE: 0429 Climate dynamics (1620)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting