HR: 1330h
AN: PP52A-0958    [PDF]
TI: Conductive Transport of Annual Temperature Signals in Variable Subsurface Media and Regional Analyses of Seasonal Decoupling Between Air and Ground Surface Temperatures
AU: * Smerdon, J E
EM: jsmerdon@umich.edu
AF: University of Michigan, Applied Physics Program 500 E. University 2477 Randall Lab, Ann Arbor, MI 48104-1120
AU: Pollack, H N
EM: hpollack@umich.edu
AF: Unversity of Michigan, Dept. of Geological Sciences 425 E. University 2534 C.C. Little Bldg., Ann Arbor, MI 48109-1063
AU: Kresl, M
EM: mkr@ig.cas.cz
AF: Geophys. Inst., Czech Academy of Sciences, 141-31 Praha 4 Sporilov Bocni II, Prague, 1401 Czech Republic
AU: Wehmiller, J F
EM: jwehm@UDel.Edu
AF: University of Delaware, Department of Geology, Newark, DE 19716
AB: Surface air temperature (SAT) and subsurface temperatures have been measured and analyzed at Fargo, North Dakota; Cape Henlopen, Delaware; Cape Hatteras, North Carolina; and Prague, Czech Republic. Data from each location have been aggregated into time series of daily means. We spectrally decompose each temperature time series into Fourier components and then determine the phase and amplitude of the isolated annual signal at each subsurface depth. The observed changes with depth in the phase and amplitude of annual signals are compared to expectations from a model of conductive heat transport in a homogeneous medium. A harmonic temperature signal propagating conductively through a homogeneous medium is characterized by a linear phase shift and exponential amplitude attenuation with depth. We show that the characteristics of propagation of the annual signals, as functions of depth below the surface, clearly indicate conductive regimes: linear regression of the phase shift and natural logarithm of the amplitude versus depth at each site yield coefficients of determination within the range 0.995-0.999. Extrapolations of regression lines to the surface yield estimates of the amplitude and phase of the annual GST signals at each location and allow comparisons to annual SAT signals. All annual GST signals are modestly attenuated and negligibly phase shifted relative to SAT; the amplitude attenuation and phase shift ranges, relative to SAT, are approximately 7.8-21.5% and 4.6-8.4 days, respectively. Amplitude attenuation is greatest in winter at Fargo and Prague where snow cover and/or subsurface freezing occur and inhibit cooling of the subsurface. Amplitude attenuation takes place in summer, however, at both Cape Hatteras and Cape Henlopen where winter effects are either negligible or absent. This attenuation is associated with summer evapotranspiration that cools the subsurface relative to the SAT. Summer or winter attenuation of annual GST signals causes increases or decreases in mean annual GST, relative to SAT, respectively. These four sites illustrate that seasonal decoupling between GST and SAT signals cannot easily be associated with a specific season at hemispheric or global scales.
DE: 1645 Solid Earth
DE: 1863 Snow and ice (1827)
DE: 3309 Climatology (1620)
DE: 3322 Land/atmosphere interactions
DE: 3344 Paleoclimatology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting