William Gosnold

The borehole temperature record of climate warming in the mid-continent of North America

Abstract Ground-surface temperature (GST) histories, determined from a carefully selected set of twenty-nine borehole temperature profiles, show a warming trend over the last century that increases systematically with latitude in the mid-continent of North America. Except one site in north Texas, the borehole locations lie within a 500 × 1000 km transect that extends from the Kansas-Nebraska border into southern Manitoba. Ground-surface warming during the last century increases from +0.4°C at 41.1°N to + 2.0°C at 49.6°N. Surface air temperature (SAT) warming in the transect, determined from Historical Climatology Network stations, increases from + 0.5°C per century at 40°C per century at 48.8°N. These warming trends agree with the regional warming pattern predicted by GCM simulations of global warming. However, the magnitudes of warming determined from the GST and the SAT data agree in regions where seasonal ground freezing does not occur but differ significantly where seasonal ground freezing does occur. Analysis of ground and air temperature coupling suggests that the greater warming observed in the GST histories in seasonally frozen ground is due to a secular increase in soil moisture that corresponds with increased precipitation during the past 50 years.

A decade of air–ground temperature exchange from Fargo, North Dakota

Abstract In borehole paleoclimatology, it is commonly assumed that a direct coupling exists between air and ground temperatures. This assumption is valid only if variables affecting ground-surface temperature exchange have remained constant through time. In an analysis of a 9-year record of air and ground temperature data, we found that several critical variables changed in ways that cause decoupling between air and ground temperatures. Mean-annual ground temperatures in the upper 12 m increased by 0.93±0.09°C during the study. Air temperatures used as model-forcing signals generated ground temperatures that exhibit no significant increase. The decoupling of winter air and ground temperatures is due to snow cover and latent energy effects. Maximum residual temperatures for freezing, summer and thawing modeling periods averaged ±0.18°C, ±0.30°C, and ±0.75°C, respectively. Duration of winter snow cover increased during the time of record and correlates with winter air–ground temperature differences (r2=0.71). Annual values of modeled latent energy of ground freezing show a dependence upon total precipitation 60 days prior to ground freezing.

Heat flow and ground water flow in the great plains of the United States

Abstract Regional groundwater flow in deep aquifers adds advective components to the surface heat flow over extensive areas within the Great Plains province. The regional groundwater flow is driven by topographically controlled piezometric surfaces for confined aquifers that recharge either at high elevations on the western edge of the province or from subcrop contacts. The aquifers discharge at lower elevations to the east. The assymetrical geometry for the Denver and Kennedy Basins is such that the surface areas of aquifer recharge are small compared to the areas of discharge. Consequently, positive advective heat flow occurs over most of the province. The advective component of heat flow in the Denver Basin is on the order of 15 mW m−2 along a zone about 50 km wide that parallels the structure contours of the Dakota aquifer on the eastern margin of the Basin. The advective component of heat flow in the Kennedy Basin is on the order of 20 mW m−2 and occurs over an extensive area that coincides with the discharge areas of the Madison (Mississippian) and Dakota (Cretaceous) aquifers. Groundwater flow in Paleozoic and Mesozoic aquifers in the Williston Basin causes thermal anomalies that are seen in geothermal gradient data and in oil well temperature data. The pervasive nature of advective heat flow components in the Great Plains tends to mask the heat flow structure of the crust, and only heat flow data from holes drilled into the crystalline basement can be used for tectonic heat flow studies.

Performance Improvements for a Large-scale Geological Simulation☆

Abstract Geological models have been successfully used to identify and study geothermal energy resources. Many computer simulations based on these models are data-intensive applications. Large-scale geological simulations require high performance computing (HPC) techniques to run within reasonable time constraints and performance levels. One research area that can benefit greatly from HPC techniques is the modeling of heat flow beneath the Earths surface. This paper describes the application of HPC techniques to increase the scale of research with a well-established geological model. Recently, a serial C++ application based on this geological model was ported to a parallel HPC applications using MPI. An area of focus was to increase the performance of the MPI version to enable state or regional scale simulations using large numbers of processors. First, synchronous communications among MPI processes was replaced by overlapping communication and computation (asynchronous communication). Asynchronous communication improved performance over synchronous communications by averages of 28% using 56 cores in one environment and 46% using 56 cores in another. Second, an approach for load balancing involving repartitioning the data at the start of the program resulted in runtime performance improvements of 32% using 48 cores in the first environment and 14% using 24 cores in the second when compared to the asynchronous version. An additional feature, modeling of erosion, was also added to the MPI code base. The performance improvement techniques under erosion were less effective.

Crustal Heatl Flow, A Guide to Measurement & Modeling

Temperature variations and thermal properties of the Earth influence many processes and features of interest to geoscientists, and a diverse array of geoscientists have used thermal data in a variety of applications. However, heat flow is a relatively small field in terms of the number of specialists—barely more than 200 worldwide—and non-specialist users of thermal data commonly lack the basic knowledge and understanding necessary to avoid errors in application and interpretation. Crustal Heat Flow, A Guide to Measurement & Modeling, by G. R. Beardsmore and J. P. Cull, promises to provide the necessary background to ensure accuracy in analysis of thermal data, and to function as a handbook for all geologists and geophysicists who analyze thermal data.