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GEOPHYSICAL RESEARCH LETTERS VOL 32 L15405 doi 10 1029 2005GL023869 2005 Variable seasonal coupling between air and ground temperatures A simple representation in terms of subsurface thermal diffusivity Henry N Pollack Jason E Smerdon and Peter E van Keken Department of Geological Sciences University of Michigan Ann Arbor Michigan USA Received 20 June 2005 accepted 7 July 2005 published 11 August 2005 1 The utility of subsurface temperatures as indicators of temperature changes at Earth s surface rests upon an assumption of strong coupling between surface air temperature SAT and ground surface temperature GST Here we describe a simple representation of this coupling in terms of a variable thermal diffusivity in the upper meter of the subsurface The variability is tied to daily SAT precipitation and snow cover but does not incorporate the physical details of these and the many other factors that influence the air ground interface in many high fidelity landsurface models Our simple model reduces the difference between observed and modeled temperatures by a factor of 3 to 4 over a model with uniform diffusivity driven only by SAT This simple representation of air ground coupling offers a means of simulating subsurface temperatures using only archived meteorological records and creates the potential for examining the long term character of air ground temperature coupling Citation Pollack H N J E Smerdon and P E van Keken 2005 Variable seasonal coupling between air and ground temperatures A simple representation in terms of subsurface thermal diffusivity Geophys Res Lett 32 L15405 doi 10 1029 2005GL023869 1 Introduction 2 Present day subsurface temperature profiles can be inverted to reconstruct temperature histories at the ground surface that span many centuries These ground surface temperature GST histories in turn are used to estimate surface air temperature SAT changes at times prior to the beginning of the instrumental record Implicit in the latter undertaking is



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