HR: 0830h
AN: GC41A-05    [Abstracts]
TI: Thermal Offset of Soil and Air Temperatures in the Great Plains of the United States: Implications for Borehole Climate Reconstruction.
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
AU: Gosnold, W D
EM: william_gosnold@und.nodak.edu
AF: Department of Geology and Geological Engineering, University of North Dakota, Box 8358, Grand Forks, ND 58202-8358 United States
AB: Previous studies have shown that the nature of the long-term coupling of air and ground temperatures varies systematically along a latitudinal gradient in the Great Plains of the United States. These variations may have significance with respect to the validity of thermophysical assumptions implicit in borehole climate reconstructions. In this study we investigate the relationship between the thermal offset of long-term soil temperatures measured at 10-cm depth and long-term shelter height air temperatures. The thermal offset (Tsoil - Tair) for the mean annual, mean winter (DJF), and mean summer (JJA) periods is examined for a 45-station network in the central and northern Great Plains of the United States (Kansas, Nebraska, South Dakota, and North Dakota). Data is obtained from the Great Plains Regional Climate Center for ten complete seasonal years running from 1 May 1993 through 30 April 2003. We examine the regional patterns of the thermal offset for the annual, winter, and summer periods based upon the ten years of data, as well as for selected years of high and low regional snowfall totals. We also consider regional variations in snowfall amount (cm) and snow cover (cm) for the same study period. Results show a systematic increase in the annual thermal offset with increasing latitude, ranging from 1° C along the southern study region limit to 4° C along the northern limit. These annual values mask a significant seasonal contrast, however. The winter thermal offset follows a strong latitudinal gradient that ranges from less than 1° C in the southwest of the region to more than 10° C in the northeast, and which is related to regional snowfall and snow cover controls. The summer thermal offset, however, follows a weaker longitudinal gradient that ranges from 0° C in the east to 3° C in the west, and which is related to regional precipitation controls. The regional thermal offset is primarily determined by the thermoinsulation effect of snow cover, along with secondary controls associated with the availability of surface soil moisture, and the release of latent heat of fusion along the advancing freezing front. Interannual variability in the thermal offset due to regional snow cover variations will be examined, and the implications of the study results for borehole climate reconstructions will be discussed.
DE: 1823 Frozen ground
DE: 1863 Snow and ice (1827)
DE: 3309 Climatology (1620)
DE: 9350 North America
SC: Global Climate Change [GC]
MN: 2005 Joint Assembly