During nocturnal cooling over land, the 10-m wind speed falls to very low values in many parts of the world while the absolute sensible heat flux increases initially after sunset but reaches a maximum before decreasing later in the night. In contrast, a one-dimensional numerical model predicts that the nocturnal wind speed is constant after an initial reduction at the evening transition. The difference between observations and the model is attributed to topographic effects which can be significant even over minor orography. Using data from exceptionally flat sites, we show that, in the absence of topography, the nocturnal wind speed is constant and the sensible heat flux tends towards a limiting value during prolonged surface cooling.

中文翻译：

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平坦地形上的夜间风速和显热通量

在夜间陆地上空降温期间，世界许多地区的 10 米风速降至非常低的值，而绝对感热通量在日落后最初增加，但在夜间晚些时候减少之前达到最大值。相比之下，一维数值模型预测夜间风速在傍晚过渡时初始降低后是恒定的。观测值和模型之间的差异归因于地形效应，即使在较小的地形上也可能显着。使用来自异常平坦地点的数据，我们表明，在没有地形的情况下，夜间风速是恒定的，并且在长时间的表面冷却过程中，显热通量趋于一个极限值。