Mississippi River Climate and Hydrology Conference

Tuesday, 14 May 2002
Sensitivity of Soil Freeze/Thaw Cycles on Surface Energy Balance
Tingjun Zhang, CIRES/Univ. of Colorado, Boulder, CO; and F. Ling
Near-surface soil freezing and thawing processes have a significant impact on soil physical and thermal properties. Soil thermal conductivity increases substantially when soil freezes depending on soil water content and soil type, while soil hydraulic conductivity decreases by several orders of magnitude. Soil freeze and thaw also release and absorb significant amount of latent heat due to soil water phase change. Changes in these properties greatly impact the soil thermal regime and ground surface temperature, and ultimately surface energy and water balance. Our recent study shows that seasonal frozen ground extent has decreased approximately 20% during the past few decades in the Northern Hemisphere. The impact of changes in soil thermal and hydraulic properties and areal extent of seasonal frozen ground on climate and weather forecast cannot be underestimated. In this study, we will use a comprehensive one-dimensional heat conduction model with phase change to investigate the sensitivity of soil freeze/thaw cycles on surface energy balance. Specifically, we will investigate the impact of the near-surface soil freeze/thaw cycle on ground surface temperature by turning on and off soil freezing/thawing processes and by changing soil type and soil water content. Changes in ground surface temperature greatly impact sensible, latent, and soil heat fluxes, outgoing longwave radiative fluxes, and surface energy balance as a whole. Results from this study will provide a preliminary assessment on the impact of soil freeze/thaw cycles on surface energy balance, and potentially on climate and weather forecasting.

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