HR: 0800h
AN: B11A-1004    [Abstracts]
TI: Water Isotopes in the GISS ModelE Land Surface Model: Implementation and Results of Coupled Runs
AU: * Aleinov, I
EM: ialeinov@giss.nasa.gov
AF: NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025 United States
AU: * Aleinov, I
EM: ialeinov@giss.nasa.gov
AF: Center for Climate Systems Research, Columbia University, 2880 Broadway, New York, NY 10025 United States
AU: Schmidt, G A
EM: gschmidt@giss.nasa.gov
AF: NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025 United States
AB: ModelE is the latest version of the Global Circulation Model (GCM), developed at NASA Goddard Institute for Space Studies (GISS). It includes the stable water isotopes H₂¹⁸O and HDO as tracers in every aspect of the model's hydrological cycle. In this paper we describe the algorithm for tracking of passive water tracers (which the stable water isotopes are) in the Land Surface Model (LSM) of GISS ModelE GCM. GISS LSM is a layer-based model. It consists of a set of horizontal physical layers which exchange water and heat. These layers include one layer of canopy, up to three layers of snow and six layers of soil. Canopy and snow may occupy only a fraction of the cell and some fraction of the canopy may be covered by snow. Our tracer tracking algorithm updates the amount of tracer in each layer separately (as opposed to ``bucket'' algorithms which mix all soil tracers and all snow tracers together). Since water passage in our LSM generally doesn't satisfy CFL condition and since water content of some layers can be very small (actually snow layers may collapse to zero depth for thin snow), some special care had to be taken to ensure that the algorithm is stable and consistent in all special cases. We perform the advection of tracers in two ``sweeps'': down and up. During the each ``sweep'' tracers are advected only at the boundaries where direction of the flow coincides with the direction of the ``sweep''. Such algorithm ensures that upstream cells always have water and, hence, the concentration of tracers is well defined. In comparison with ``bucket'' approach our algorithm is more responsive to change of isotope concentration in precipitation and is expected to provide more accurate concentration of isotopes in evapotranspiration and runoff. We discuss results for the soil isotopes from a number of full GCM runs. In particular, we focus upon the spin up and equilibrium behavior of the isotope fields in a present day (ca. 1980) control run and the response of the isotopes to forcings over transient AMIP-style 20th Century simulations. In addition, we investigate whether the isotope fields are affected by a change in the runoff algorithm, and so examine whether the isotope fields have the potential to constrain model land surface physics.
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
DE: 1843 Land/atmosphere interactions (1218, 1631, 3322)
DE: 1847 Modeling
DE: 1866 Soil moisture
SC: Biogeosciences [B]
MN: Fall Meeting 2005