A study of turbulent fluxes and their measurement errors for different wind regimes over the tropical Zongo glacier (16° S) during the dry season
A study of turbulent fluxes and their measurement errors for different wind regimes over the tropical Zongo glacier (16° S) during the dry season
复制标题
热带宗戈冰川（南纬 16°）旱季不同风况下湍流通量及其测量误差的研究
DOI：
--
复制
发表时间：
2015
期刊：
影响因子：
--
通讯作者：
W. Helgason
中科院分区：
文献类型：
--
作者：
M. Litt;J. Sicart;W. Helgason
抽象的。在外部热带的冰川，在干燥的冬季，湍流通量是一个重要的汇融化的能量，由于高升华率，但在偏远和复杂的地形稳定的表层测量仍然具有挑战性。用涡度相关（EC）和整体空气动力学（BA）方法估算了玻利维亚热带Zongo冰川消融区（16° S，5080 m a.s.l.）的感热和潜热的表面湍流热通量，2007年7月22日至9月1日。我们研究了湍流通量及其相关的随机和系统的测量误差下的三个最常见的风制度。对于夜间密度驱动的下斜流，以及与大尺度强迫相关的强下坡流，H通常加热表面（即为正），而LE使其冷却（即为负）。平均而言，这两种通量表现出相似的大小，并相互抵消。大多数能量损失，通过湍流发生在白天上坡流，当H是弱的，由于温度梯度小，LE是强烈的负，由于非常干燥的空气。BA方法的平均随机误差（6%的净H + LE通量）主要源于粗糙度长度的大的不确定性。对于EC通量，平均随机误差主要是由于大尺度外层涡旋（12%）的统计抽样差。BA方法是高度敏感的方法，用于从长波辐射测量和低估通量，由于在低高度的垂直通量发散和湍流的非平稳性获得表面温度。EC方法也可能低估了通量，尽管程度较轻，由于低估了垂直风速和垂直通量发散。对于这两种方法，当H和LE在下坡通量中相互补偿时，偏差往往相互抵消或保持较小。当净湍流通量（H + LE）是最大的上坡流，非平稳效应和低估的垂直风速不补偿，表面温度误差是重要的，所以大的偏差H + LE时，预计使用EC和BA方法。
Abstract. Over glaciers in the outer tropics, during the dry winter season, turbulent fluxes are an important sink of melt energy due to high sublimation rates, but measurements in stable surface layers in remote and complex terrains remain challenging. Eddy-covariance (EC) and bulk-aerodynamic (BA) methods were used to estimate surface turbulent heat fluxes of sensible (H) and latent heat (LE) in the ablation zone of the tropical Zongo Glacier, Bolivia (16° S, 5080 m a.s.l.), from 22 July to 1 September 2007. We studied the turbulent fluxes and their associated random and systematic measurement errors under the three most frequent wind regimes. For nightly, density-driven katabatic flows, and for strong downslope flows related to large-scale forcing, H generally heats the surface (i.e. is positive), while LE cools it down (i.e. is negative). On average, both fluxes exhibit similar magnitudes and cancel each other out. Most energy losses through turbulence occur for daytime upslope flows, when H is weak due to small temperature gradients and LE is strongly negative due to very dry air. Mean random errors of the BA method (6 % on net H + LE fluxes) originated mainly from large uncertainties in roughness lengths. For EC fluxes, mean random errors were due mainly to poor statistical sampling of large-scale outer-layer eddies (12 %). The BA method is highly sensitive to the method used to derive surface temperature from longwave radiation measurements and underestimates fluxes due to vertical flux divergence at low heights and nonstationarity of turbulent flow. The EC method also probably underestimates the fluxes, albeit to a lesser extent, due to underestimation of vertical wind speed and to vertical flux divergence. For both methods, when H and LE compensate each other in downslope fluxes, biases tend to cancel each other out or remain small. When the net turbulent fluxes (H + LE) are the largest in upslope flows, nonstationarity effects and underestimations of the vertical wind speed do not compensate, and surface temperature errors are important, so that large biases on H + LE are expected when using both the EC and the BA method.