HR: 1020h
AN: PP52A-0651    [Abstracts]
TI: Relationship Between Snow Cover and Thermal Offset of Soil and Air Temperatures in the Great Plains of the United States.
AU: * Todhunter, P E
EM: paul_todhunter@und.nodak.edu
AF: Department of Geography, University of North Dakota, Box 9020, Grand Forks, ND 58202-9020 United States
AU: Popham, J L
EM: popham@aero.und.edu
AF: Department of Atmospheric Sciences, University of North Dakota, Box 9006, Grand Forks, ND 58202-9006 United States
AB: Previous studies have shown that the coupling of air and soil temperatures along a latitudinal gradient in the Great Plains of the United States varies systematically due to the thermoinsulatory effect of snow cover and the release of latent heat of fusion along the freezing front. These variations may be significant for the assumptions made in the use of borehole climate reconstructions. We examine the thermal offset (Tsoil - Tair) of shelter-height and 10-cm soil temperatures for a 45-station network in the central and northern Great Plains for ten complete seasonal cycles running from 1 May 1993 through 30 April 2003. We then compare these results with a 42-station daily snow cover dataset for the same region, and summarize the results for the mean annual thermal offset, as well as for the mean winter (DJF) and summer (JJA) offsets. We compare the mean fields for the 10-year period with individual fields for the years with the maximum and minimum winter snow covers to determine the effect of interannual variability of snow cover upon the thermal offset of soil and air temperatures. The mean annual thermal offset varies from less than 1°C in the southern limits of the study region to more than 4°C in the northern limits. The mean number of days with measurable snow cover at the time of observation ranges from 15 to 140 days. The mean annual thermal offset, however, is strongly controlled by the magnitude of the mean winter thermal offset, which in turn is sensitive to variations in the duration and depth of the snow cover. Examining the mean annual thermal offset obscures this effect because soil and air temperature coupling is controlled by different physical mechanisms during the warm season. Mean winter thermal offset for the individual winter with maximum snow cover ranged from less than 1°C to more than 14°C, but by only 1°C to 8°C for the minimum snow cover year. The thermal offset is found to be insensitive to snow cover variations in the central Great Plains, but sensitive by a factor of two in the northern Great Plains.
DE: 0700 CRYOSPHERE (4540)
DE: 0704 Seasonally frozen ground
DE: 0736 Snow (1827, 1863)
DE: 0768 Thermal regime
DE: 1637 Regional climate change
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005