HR: 08:00h
AN: C31A-01    [Abstracts]
TI: Cold-Region Subsurface Hydro-thermal Sensitivity of Physical Land Scheme in Global Climate Model: Idealized Off-Line Evaluation
AU: * Saito, K
EM: ksaito@iarc.uaf.edu
AF: International Arctic Research Center University of Alaska Fairbanks, 930 Koyukuk Dr. 408B Akasofu Bldg. PO Box 757340, Fairbanks, AK 99775-7340, United States
AU: * Saito, K
EM: ksaito@iarc.uaf.edu
AF: Frontier Research Center for Global Change Japan Agency of Marine-Earth Science and Technology, 3173-25 Syowa-machi Kanazawa-ku, Yokohama, 236-0001, Japan
AB: There have been a number of successful works and accumulation of experiences to understand the subterranean surface hydro-thermal processes in the cold regions, and to quantize by numerical physical models, targeted to specific plots to sub-catchments. However, for most of the land surface schemes in regional to global models improvement and optimizations seems necessary to realize required performance, in terms of the complexity of the resolved physical processes and properties, and the initial and boundary conditions. A series of 100-year sensitivity experiments were conducted with a land surface scheme (MATSIRO) in a coupled global climate model (GCM), CCSR/NIES/FRCGC MIROC v3.2, to provide information for the future refinement directions. To evaluate the model performance under climatological and warming conditions, two sets of idealized meteorological forcing were prepared, based on the observations taken at Barrow, AK for 1990 through 2003, for the 1990s climatology and the incremental warming condition with about 6 degree C per century. Quantitative impact of the following factors were investigated in the experiments: 1) total depth of the soil column, and the layer thickness in the top layers, 2) presence of organic layers close to the surface, 3) porosity profile of the soil column, 4) amount of precipitation, and 5) physical parameterization of the thermal and hydrological properties, namely consideration of co-existence of solid and liquid water under the freezing point. Major results and their implications include the following. Total depth of 20m or deeper would be necessary to provide appropriate thermal buffer and to justify the constant geothermal flux boundary conditions at the bottom, which also improved the seasonal cycle of simulated subsurface thermal regimes by eliminating numerical flaws resulted from a too shallow soil column. Inclusion of organic layers improved the thickness of maximum active layer, and suppressed its unrealistic increase under warming: more than doubled without organic layers, compared to 46% increase when included. Porosity profile showed little impact, although it could have affected total capacity and permeability of heat and water of the soil. Refined thermal parameterization improved the seasonal evolution of active layer thickness, and decelerated the change under warming conditions. With intensified precipitation, permanently unfrozen layers were formed above permafrost table in the warming experiments.
DE: 0702 Permafrost (0475)
DE: 1621 Cryospheric change (0776)
DE: 1626 Global climate models (3337, 4928)
SC: Cryosphere [C]
MN: 2007 Fall Meeting