Energy and surface moisture seasonally limit evaporation and sublimation from snow-free alpine tundra
Energy and surface moisture seasonally limit evaporation and sublimation from snow-free alpine tundra
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DOI：
10.1016/j.agrformet.2012.01.017
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发表时间：
2012-05-15
影响因子：
6.2
通讯作者：
Chowanski, Kurt M.
中科院分区：
文献类型：
--
作者：
Knowles, John F.;Blanken, Peter D.;Chowanski, Kurt M.
该研究强调了景观位置和由此产生的积雪对无雪高山冻土带水文平衡的重要性，并建议建模研究必须考虑能量平衡的季节性不同分配，以便准确预测蒸发和/或升华。利用涡旋相关方差法对2007 - 2009年CO . Niwot Ridge高海拔（海拔3502 m）高山冻土带地表能量平衡进行了3年的观测。冬季场地以风蚀为主，积雪较少。两个共存的塔提供了限制复杂山地地形对测量不确定度的影响的机会，总体误差与其他FLUXNET站点相当。湍流通量的随机测量不确定度约为夏季正午值的10%。在整个测量期间，0.5 h平均能量平衡关闭率为81%，在夏季湍流通量较大时，能量平衡关闭率提高到91%。年平均降水量为955 mm，但24 h平均蒸发分数为0.39，为典型的干草地或草地生态系统。这些低值归因于整个冬季盛行的大风条件快速有效地清除了积雪。在降雨提供水分的夏季，蒸发主要受可用能量的限制。总体而言，年降水量的平均39%被蒸发或升华回大气。我们认为降水的年分布对该生态系统的蒸发和升华起着重要的控制作用。(c) 2012 Elsevier B.V.版权所有
This study highlights the importance of landscape position and resultant snow accumulation to the hydrologic balance of snow-free alpine tundra, and suggests that modeling studies must account for seasonally dissimilar partitioning of the energy balance in order to accurately predict evaporation and/or sublimation. The eddy covariance method was used to measure the surface energy balance above high-elevation (3502 m above sea level) alpine tundra at Niwot Ridge, CO, over 3 years from 2007 to 2009. During the winter the site was characterized by wind scour, with little snow accumulation. Two co-located towers afforded the opportunity to constrain the influence of complex mountain topography on measurement uncertainty, and overall errors were comparable to other FLUXNET sites. Random measurement uncertainty for the turbulent fluxes was approximately 10% of midday summertime values. The 0.5-h mean energy balance closure was 81% over the entire measurement period, and improved to 91% during the summer when the magnitude of the turbulent fluxes was larger. In spite of 955 mm mean annual precipitation, the 24-h mean evaporative fraction was 0.39, typical of dry grassland or rangeland ecosystems. These low values were attributed to rapid, efficient removal of snow by prevailing windy conditions throughout the winter. During the summer when rainfall provided moisture, evaporation was principally limited by available energy. Overall, an average of 39% of annual precipitation was evaporated or sublimated back to the atmosphere. We conclude that the annual distribution of precipitation is an essential control on evaporation and sublimation from this ecosystem. (c) 2012 Elsevier B.V. All rights reserved.