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Spatial and temporal variations in near-surface energy fluxes in an Alpine valley under synoptically undisturbed and clear-sky conditions
Quarterly Journal of the Royal Meteorological Society ( IF 3.0 ) Pub Date : 2021-03-09 , DOI: 10.1002/qj.4016 Manuela Lehner 1 , Mathias W. Rotach 1 , Eleni Sfyri 1 , Friedrich Obleitner 1
Quarterly Journal of the Royal Meteorological Society ( IF 3.0 ) Pub Date : 2021-03-09 , DOI: 10.1002/qj.4016 Manuela Lehner 1 , Mathias W. Rotach 1 , Eleni Sfyri 1 , Friedrich Obleitner 1
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Diurnal cycles of turbulent sensible and latent heat fluxes are typically closely related to the diurnal cycles of solar irradiation under synoptically undisturbed and clear-sky conditions. In mountainous terrain, large variations can occur in the topographic and surface properties, which modify the local radiation budget and thus turbulent energy fluxes and the surface energy balance. Another characteristic of mountainous terrain is local, thermally driven circulation systems, such as the slope- and valley-wind system, which can equally affect turbulent exchange. Observations of near-surface radiative and turbulent fluxes are presented from six eddy-covariance stations in an approximately east–west-oriented major Alpine valley for undisturbed and clear-sky conditions. Median diurnal cycles over the whole year are compared at the six sites and related to local terrain characteristics and the thermally driven wind systems. At a scale that is smaller than grid cells in current operational global forecast models, heat, moisture, and momentum fluxes show a large spatial variability in the magnitudes and their diurnal cycles. Lowest heat fluxes are observed on the north-facing sidewall, where solar irradiation and thus available energy are reduced compared with the valley floor and south-facing sidewall. Differences in the land surface characteristics further affect the partitioning of the available energy into sensible and latent heat fluxes. The median sensible heat flux reaches its daily peak already before solar noon at several sites, which appears to be related to the transition from down-valley to up-valley winds. In contrast to flat and homogeneous terrain, horizontal heat fluxes and lateral momentum fluxes can reach magnitudes that are similar to the magnitudes of vertical heat fluxes and longitudinal momentum fluxes, respectively.
中文翻译：
天气未受干扰和晴空条件下阿尔卑斯山谷近地表能量通量的时空变化
湍流感热通量和潜热通量的昼夜循环通常与天气未受干扰和晴空条件下太阳辐射的昼夜循环密切相关。在山区，地形和地表特性会发生很大变化，这会改变局部辐射收支，从而改变湍流能量通量和表面能量平衡。山区地形的另一个特征是局部的热驱动循环系统，例如斜坡和山谷风系统，它们同样会影响湍流交换。近地表辐射和湍流通量的观测来自位于一个大致东西向的主要高山山谷的六个涡旋协方差站，在不受干扰和晴朗的天空条件下。对六个地点全年的中值昼夜循环进行了比较，并与当地地形特征和热驱动风系统有关。在当前全球运营预测模型中，在小于网格单元的尺度上，热量、水分和动量通量在幅度和昼夜循环方面表现出很大的空间变异性。在朝北的侧壁上观察到最低的热通量，与谷底和朝南的侧壁相比，这里的太阳辐射和可用能量减少。地表特征的差异进一步影响可用能量分配为感热通量和潜热通量。几个地点的中值感热通量在太阳正午之前就已达到每日峰值，这似乎与从山谷下风到山谷上风的转变有关。与平坦且均质的地形相比，水平热通量和横向动量通量的幅度分别与垂直热通量和纵向动量通量的幅度相似。
更新日期：2021-03-09
中文翻译：
天气未受干扰和晴空条件下阿尔卑斯山谷近地表能量通量的时空变化
湍流感热通量和潜热通量的昼夜循环通常与天气未受干扰和晴空条件下太阳辐射的昼夜循环密切相关。在山区，地形和地表特性会发生很大变化，这会改变局部辐射收支，从而改变湍流能量通量和表面能量平衡。山区地形的另一个特征是局部的热驱动循环系统，例如斜坡和山谷风系统，它们同样会影响湍流交换。近地表辐射和湍流通量的观测来自位于一个大致东西向的主要高山山谷的六个涡旋协方差站，在不受干扰和晴朗的天空条件下。对六个地点全年的中值昼夜循环进行了比较，并与当地地形特征和热驱动风系统有关。在当前全球运营预测模型中，在小于网格单元的尺度上，热量、水分和动量通量在幅度和昼夜循环方面表现出很大的空间变异性。在朝北的侧壁上观察到最低的热通量，与谷底和朝南的侧壁相比，这里的太阳辐射和可用能量减少。地表特征的差异进一步影响可用能量分配为感热通量和潜热通量。几个地点的中值感热通量在太阳正午之前就已达到每日峰值，这似乎与从山谷下风到山谷上风的转变有关。与平坦且均质的地形相比，水平热通量和横向动量通量的幅度分别与垂直热通量和纵向动量通量的幅度相似。
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