HR: 1340h
AN: A43D-1577    [Abstracts]
TI: Comparative Hydrology Over Monsoonal Regions Using Seasonal Distributions of Stable Water Isotopes.
AU: * Brown, D P
EM: derek.brown@colorado.edu
AF: Program in Atmospheric and Oceanic Sciences and Cooperative Institute for Research in Environmental Sciences, University of Colorado at Boulder, Campus Box 216 University of Colorado, Boulder, CO 80309-0216, United States
AU: Worden, J
EM: john.worden@jpl.nasa.gov
AF: Jet Propulsion Laboratory, M/S 183-601 4800 Oak Grove Drive, Pasadena, CA 91109, United States
AU: Noone, D C
EM: dcn@colorado.edu
AF: Program in Atmospheric and Oceanic Sciences and Cooperative Institute for Research in Environmental Sciences, University of Colorado at Boulder, Campus Box 216 University of Colorado, Boulder, CO 80309-0216, United States
AB: The hydrologic regimes of monsoonal regions contain complex balances of large-scale advective supply of water, surface exchange and atmospheric condensation, which are important for the regional energy balance and climate. Stable water isotopes are powerful tools for studying such processes, as isotopic fractionations occurring during evaporation and condensation give rise to measurable variations in the isotopic composition that reflects the history of moist processes for each observed air parcel. The HDO/H2O data set from the Tropospheric Emission Spectrometer (TES) on NASA's Aura spacecraft offers a unique global view of the isotopic composition of water vapor. The TES data set, and the analysis here, is complimentary to previous work using isotopic ratios in precipitation; however it need not be that the simple relationships found in the precipitation data hold for the atmospheric vapor case because of the variability induced by atmospheric mixing and convection. Over tropical continents, the intensity of water vapor recycling, precipitation rates and circulation patterns are thought to dominate the seasonal isotopic composition of water vapor and rainfall. By examining and contrasting the isotopic budgets of the Amazon, north Australia, and Asian monsoon regions, we gain insight into these hydrological processes, show which processes are regionally robust, and expose those processes that are regionally unique. To establish the importance of local processes on the regional isotopic composition, we first examine the relationship between the measured isotopic composition and meteorological parameters that capture the strength of the local processes. Secondly, we use the history of condensation, evaporation and air mass mixing during transport from five-day origin locations to the local TES observations, and the isotopic ratios of vapor at both locations, to examine isotopic changes that occur upstream. Using this information, as well as a simple isotopic exchange model that uses the isotopic ratios as constraints, we provide a unique view of the seasonal contributions of moisture via an evaporative source versus the losses due to condensation. Our results show that during the monsoonal seasons of the regions studied, additional isotopic exchange during intense condensation or through rainfall evaporation can explain the substantial isotopic depletion that deviates from the Rayleigh distillation model. Secondly, we show that local convection introduces intra-seasonal variability in the regional isotopic ratios, which shows local sources of moisture are significant for each region. Thirdly, the isotopic composition reveals substantial subsidence for the dry seasons of the Asian monsoon and N. Australian regions, indicating a seasonal source of dry air. Our results reveal that the regional ratios of moisture gain from an evaporative source versus the moisture loss from condensation vary from close to zero for the wettest months to unity for the dry seasons. These results show that the isotopic ratios of water vapor can further the understanding of the physics of regional hydrology near monsoonal areas.
DE: 1818 Evapotranspiration
DE: 1843 Land/atmosphere interactions (1218, 1631, 3322)
DE: 1876 Water budgets
DE: 3309 Climatology (1616, 1620, 3305, 4215, 8408)
DE: 3360 Remote sensing
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting