Abstracts
SEARCH Open Science Meeting
October 27, 2003
Seattle, Washington, USA
Modeling Evidence for Recent Warming of the Arctic Soil Thermal Regime as Derived with a Finite-Difference Heat-Conduction Model
Christoph Oelke1, Tingjun Zhang2, Mark C. Serreze3
1National Snow and Ice Data Center (NSIDC), CIRES, University of Colorado, C.B. 449, Boulder, CO, 80309, USA, Phone 303-735-0213, Fax 303-492-2468, coelke@nsidc.org
2National Snow and Ice Data Center (NSIDC), CIRES, University of Colorado, C.B. 449, Boulder, CO, 80309, USA, Phone 303-492-5236, Fax 303-492-2468, tzhang@nsidc.org
3National Snow and Ice Data Center (NSIDC), CIRES, University of Colorado, C.B. 449, Boulder, CO, 80309, USA, Phone 303-492-2963, Fax 303-492-2468, serreze@nsidc.org
A finite difference model for one-dimensional heat conduction with phase change is applied to investigate soil freezing and thawing processes over the Arctic drainage basin. Calculations are performed on the 25 km x 25 km resolution NSIDC EASE-Grid. NCEP re-analyzed sigma-0.995 surface temperature with a topography correction, and SSM/I-derived weekly snow heights are used as forcing parameters. The importance of using an annual cycle of snow density for different snow classes is emphasized. Soil bulk density and the percentages of silt/clay and sand/gravel are from the SoilData System of the International Geosphere Biosphere Programme. In addition, we parameterize a spatially variable peat layer using specific soil bulk density and thermal conductivity. Climatological soil moisture content is from the Permafrost/Water Balance Model at the University of New Hampshire.
The model domain is divided into 3 layers with distinct thermal properties of frozen and thawed soil, respectively. Calculations are performed on 63 model nodes ranging from a thickness of 10 cm near the surface to 2 m at 30 m depth, the lower model boundary. Initial temperatures are chosen according to the grid cell's IPA permafrost classification and the model is then spun up for 52 years in order to obtain realistic start conditions for temperatures on all model layers.
The soil model is run for the 22-year period 1980 through 2001 with a daily time step. We present results for soil temperature at different depths for the whole Arctic terrestrial drainage, and for active layer depth in permafrost regions. Simulated thaw depths are compared to late-summer measurements made at 66 CALM field sites within the continuous and discontinuous permafrost regions. A remaining RMS-error between modeled and measured values is attributed mainly to scale discrepancies (100 m x 100 m vs. 25 km x 25 km) based on differences in the fields of air temperature, snow height, and soil bulk density. Also annual soil temperature cycles at different depths compare fairly well with measurements in Alaska and Siberia. Trends in active-layer depth and in soil temperatures at different depths are set into relationship with trends in air temperature and snow forcing data, and reveal a clear warming trend of the Arctic soil thermal regime over the past 20+ years. These trends are positive for all permafrost regions and largest for the region of continuous permafrost with a warming of about 0.03 K/yr at the surface. Seasonal soil surface temperature trends as high as 0.05 K/yr are found for spring and for fall, but winter and summer trends are lower with about 0.02 K/yr. The warming rate for continuous permafrost regions has increased to about 0.15 K/yr for the last eight years of the time series (1994-2001).
Abstract Categories: Changes on Land
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