Nocturnal Near-Surface Temperature, but not Flow Dynamics, can be Predicted by Microtopography in a Mid-Range Mountain Valley
Nocturnal Near-Surface Temperature, but not Flow Dynamics, can be Predicted by Microtopography in a Mid-Range Mountain Valley
复制标题
DOI：
10.1007/s10546-017-0281-y
复制
发表时间：
2017-11-01
影响因子：
4.3
通讯作者：
Thomas, Christoph K.
中科院分区：
文献类型：
--
作者：
Pfister, Lena;Sigmund, Armin;Thomas, Christoph K.
我们调查夜间流动动力学和温度行为的表面附近的一个170米长的缓坡在中程山谷。与许多现有的研究集中在具有显著地形变化的地点相比，缓坡覆盖了地球表面更大的空间范围。在地面以上最低一米处的二维光纤阵列内使用高分辨率分布式温度传感方法测量气温。主要目标是表征近地表温度和流动动力学的时空模式，并量化它们对微地形和土地覆盖的响应。在实验期间，甚至包括有弱风和强辐射强迫的晴朗天空夜晚，理论预测的经典冷空气排放都无法检测到。相比之下，我们表明，气流的两个主要的流动模式起源于非本地。最丰富的流动模式的特点是垂直解耦层具有近地面流垂直于斜坡和强大的稳定分层，这与当地生产的冷空气的重力驱动的下坡流的预期。微地形和土地覆盖的差异明显影响时空温度扰动。第二个最丰富的流动模式的特点是强烈的混合，导致垂直耦合与气流直接向下的局部斜坡。在这里，微地形和土地覆盖的变化导致可以忽略不计的近地表温度扰动。我们的结论是，时空温度扰动，但不是流动动力学，可以预测的微地形，这使得预测的对流热成分和存在和动态的冷空气池在缓坡地形中的观测情况下，复杂化。
We investigate nocturnal flow dynamics and temperature behaviour near the surface of a 170-m long gentle slope in a mid-range mountain valley. In contrast to many existing studies focusing on locations with significant topographic variations, gentle slopes cover a greater spatial extent of the Earth's surface. Air temperatures were measured using the high-resolution distributed-temperature-sensing method within a two-dimensional fibre-optic array in the lowest metre above the surface. The main objectives are to characterize the spatio-temporal patterns in the near-surface temperature and flow dynamics, and quantify their responses to the microtopography and land cover. For the duration of the experiment, including even clear-sky nights with weak winds and strong radiative forcing, the classical cold-air drainage predicted by theory could not be detected. In contrast, we show that the airflow for the two dominant flow modes originates non-locally. The most abundant flow mode is characterized by vertically-decoupled layers featuring a near-surface flow perpendicular to the slope and strong stable stratification, which contradicts the expectation of a gravity-driven downslope flow of locally produced cold air. Differences in microtopography and land cover clearly affect spatio-temporal temperature perturbations. The second most abundant flow mode is characterized by strong mixing, leading to vertical coupling with airflow directed down the local slope. Here variations of microtopography and land cover lead to negligible near-surface temperature perturbations. We conclude that spatio-temporal temperature perturbations, but not flow dynamics, can be predicted by microtopography, which complicates the prediction of advective-heat components and the existence and dynamics of cold-air pools in gently sloped terrain in the absence of observations.