Characteristics of land surface heat and water exchange under different soil freeze/thaw conditions over the central Tibetan Plateau (pages 2531–2541)

摘要

Freezing and thawing processes at the soil surface play an important role in determining the nature of Tibetan land andnatmosphere interactions. In this study, land surface water and heat exchanges under different freezing and thawing conditionsnover the central Tibetan Plateau were investigated using observations from the Coordinated Enhanced Observing Period/Asia-nAustralia Monsoon Project on the Tibetan Plateau, and the Simultaneous Heat and Water Model. During the freezing andnthawing stages, significant diurnal variation of soil temperature resulted in a diurnal cycle of unfrozen water content at thensurface. Radiation and energy components and evapotranspiration averaged over four freeze/thaw stages also changed diurnally.nOn average, the surface albedo (0D68) during the completely frozen stage was sharply higher than those during the freezing,nthawing, and completely thawed stages due to the snow cover. The Bowen ratios were 3D1 and 2D5 in the freezing and thawingnstages, respectively, but the ratio was only 0D5 in the completely thawed stage. Latent heat flux displayed distinctly betterncorrelation with unfrozen soil water content during the freezing and thawing stages than during the completely frozen andnthawed stages. This implies that the diurnal cycle of unfrozen soil water, resulting from diurnal freeze/thaw cycles at thensurface, has a significant impact on latent heat flux. A surface energy imbalance problem was encountered, and the possiblensources of error were analysed. Copyright  2011 John Wiley & Sons, Ltd.