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In Situ Monitoring of Soil Thermal Properties and Heat Flux during Freezing and Thawing
Author(s) -
Ochsner Tyson E.,
Baker John M.
Publication year - 2008
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2007.0283
Subject(s) - heat flux , eddy covariance , latent heat , soil thermal properties , flux (metallurgy) , snowmelt , sensible heat , energy balance , volumetric heat capacity , environmental science , heat transfer , thermal conductivity , atmospheric sciences , materials science , thermodynamics , soil water , soil science , snow , meteorology , geology , hydraulic conductivity , ecosystem , physics , ecology , biology , metallurgy
When soil freezes or thaws, latent heat fluxes occur and conventional methods for monitoring soil heat flux are inaccurate, often wildly so. This prevents the forcing of surface energy balance closure that is used in Bowen ratio flux measurements and the assessment of closure that is used as a check on the accuracy of eddy covariance measurements. We hypothesized that heat pulse sensors could be used to obtain accurate measurements of apparent thermal conductivity (λ a ) and apparent volumetric heat capacity ( C a ), which, together with soil temperature data, would permit accurate monitoring of soil heat flux under freezing and thawing conditions. Wintertime apparent thermal properties were monitored in situ using heat pulse sensors and independently predicted using a theoretical model. The measurements and the model both showed that for temperatures between −5 and 0°C, λ a and C a were strongly temperature dependent, varying more than two orders of magnitude. This temperature dependence is primarily the result of latent heat transfer processes. Good agreement existed between the measured and modeled thermal properties, with mean absolute differences of 20% for C a and 37% for λ a Measured and modeled soil heat flux during spring thaw and snowmelt were similar, with cumulative totals differing by only 6% during a 7‐d period. During that same period, we measured a latent heat flux into the soil of 7.9 MJ m −2 , a sizeable heat flux completely undetectable by previous methods. The results of this study support our hypothesis and indicate that this method may be useful in wintertime surface energy balance studies.