Differences between repeated borehole temperature logs in the southern Canadian Prairies-validating borehole climatology

International audienceTemperature-depth (T-z) profiles from twenty-four shallow boreholes of less than 250 m in depth located in flat, semi-arid areas of the southern Canadian Prairie Provinces initially measured in the late 1980's and early 1990's and repeated between 2004 and 2006 show strong ground surface temperature (GST) warming signatures. GST changes of 0.1?0.2°C, and 0.4°C, are observed between the measurements for the shorter (decade) and longer (two decades) time spans, respectively. Borehole sites with repeated temperature logs are selected to demonstrate that multiple T-z profiles provide general agreement between GST warming and observed surface air temperature (SAT) warming measured at nearby historical climate stations. A comparison of measured changes from repeated temperature logs with those simulated from SAT forcing demonstrates the influence of SAT on the observed deviation of temperature with depth despite variations in snow cover. Repeated borehole measurements from the northern Great Plains of the USA also identify a similar positive temperature change but of lower magnitude. Temperature changes since 1900 in the southern Canadian Prairies and the adjoining northern Great Plains of the USA, as derived from the functional state inversion (FSI) of deeper borehole logs, average 2.5°C but show a strong latitudinal gradient

Conduction‐dominated heat transport of the annual temperature signal in soil

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95182/1/jgrb13727.pd

Air-ground temperature coupling and subsurface propagation of annual temperature signals

Borehole-based reconstructions of ground surface temperature (GST) have been widely used as indicators of paleoclimate. These reconstructions assume that heat transport within the subsurface is conductive. Climatic interpretations of GST reconstructions also assume that GST is strongly coupled to surface air temperature (SAT) on timescales of decades and longer. We examine these two assumptions using records of SAT and subsurface temperature time series from Fargo, North Dakota; Prague, Czech Republic; Cape Henlopen State Park, Delaware; and Cape Hatteras National Seashore, North Carolina. The characteristics of downward propagating annual temperature signals at each site clearly indicate that heat transport can be described as one-dimensional conduction in a homogeneous medium. Extrapolations of subsurface observations to the ground surface yield estimates of annual GST signals and allow comparisons to annual SAT signals. All annual GST signals are modestly attenuated and negligibly phase shifted relative to SAT. The four sites collectively demonstrate that differences between annual GST and SAT signals arise in both summer and winter seasons, in amounts dependent on the climatic setting of each site

Daily, seasonal, and annual relationships between air and subsurface temperatures

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95285/1/jgrd11942.pd

Exploration for hot dry rock geothermal resources in the Midcontinent USA

Volume 1 consists of an introduction, a geologic overview of the Midcontinent, and data acquisition and evaluation. Volume 2 contains a section on conceptual models for hot dry rock geothermal exploration; local test site evaluations of geothermal prospects in western Nebraska, the Mississippi Embayment area, and southeastern Michigan; and studies related to the deep drill holes in northern Illinois.W. J. Hinze, L. W. Braile, R. R. B. von Frese, E. G. Lidiak, R. E. Denison, G. R. Keller, R. F. Roy, C. A. Swanberg, C. L. V. Aiken, P. Morgan with contributions from W. D. Gosnold.Abstract -- Introduction -- Geologic overview -- Data acquisition and evaluation -- Heat-flow map of the united states based on silica geothermometry -- HDR midcontinent aeromagnetic index -- Hot dry rock conceptual models for exploration strategy -- HDR test site investigations -- The Illinois deep drill hole project -- Introduction to the Illinois deep hole project -- Petrology and physical properties of granites from the Illinois deep hole in Stephenson county -- Geological significance of surface gravity measurements in the vicinity of the Illinois deep drill holes