HR: 0830h
AN: C41B-0971    [PDF]
TI: Inter-Decadal Variations of the Near-Surface Freeze/Thaw Cycle of Soils in the Northern Hemisphere
AU: * Zhang, T
EM: tzhang@nsidc.org
AF: National Snow and Ice Data Center, CIRES, 449 UCB University of Colorado, Boulder, CO 80309-0449 United States
AU: Armstrong, R
EM: rlax@nsidc.org
AF: National Snow and Ice Data Center, CIRES, 449 UCB University of Colorado, Boulder, CO 80309-0449 United States
AB: Understanding of the near-surface freeze/thaw cycle of soils is prerequisite for evaluating the impact of cold season/cold region processes on surface and subsurface hydrology, regional and global climate, carbon exchange between the atmosphere and the land, and the terrestrial ecosystem as a whole. Change in the freeze/thaw cycle of soils is also a good indicator and integrator of climate and environmental change. A frozen soil algorithm was developed at the National Snow and Ice Data Center to detect the near-surface soil freeze/thaw cycle over snow-free and snow-cover land surface. The frozen soil algorithm consists of two parts: (i) over snow-free land areas, passive microwave satellite remote sensing algorithm was used to detect the near-surface soil freeze-thaw cycle; (ii) over snow-covered land areas, a one-dimensional numerical heat transfer model with phase change was used to detect soil freeze-thaw status under snow cover. The frozen soil algorithm has been validated with the accuracy of approximately 83 percent in the contiguous United States. The frozen soil algorithm was applied to investigate the near-surface soil freeze-thaw status in the Northern Hemisphere for the period from 1978 through 2002. Passive microwave satellite remote sensing data of SMMR and SSM/I are used in the analysis. The timing, area extent, frequency, and length of the near-surface soil freeze period are investigated. The preliminary results indicate that the maximum area extent of frozen ground can be up to 60 percent of the exposed land surface with significant inter-annual variations in the Northern Hemisphere. The duration of the seasonally frozen ground ranges from less than one month in the south to over eight months in high altitude and latitude regions. The actual number of days of soil freezing varies from a few weeks to more than several months. The near-surface soil freeze/thaw cycle is characterized by low frequency (less than 5 times per winter) and long duration (greater than 2 months per cycle) at high elevation and latitude regions, by high frequency (greater than 10 times per winter) and short duration (less than 2 weeks per cycle) in the middle latitudes, and by low frequency (less than 5 times per winter) and short duration (less than 2 weeks per cycle) in lower latitude regions. The time series (1978-2002) analysis indicates that in general maximum area extent decreased and the last date of soil freezing in spring became earlier, while there were significant variations from different regions.
DE: 1600 GLOBAL CHANGE (New category)
DE: 1640 Remote sensing
DE: 1823 Frozen ground
DE: 1863 Snow and ice (1827)
SC: Cryosphere [C]
MN: 2003 Fall Meeting