The Causes of Foehn Warming in the Lee of Mountains
The Causes of Foehn Warming in the Lee of Mountains
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DOI：
10.1175/bams-d-14-00194.1
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发表时间：
2016-03-01
影响因子：
8
通讯作者：
Renfrew, Ian A.
中科院分区：
文献类型：
--
作者：
Elvidge, Andrew D.;Renfrew, Ian A.
焚风效应是众所周知的变暖，干燥，和云清除经验的背风侧山脉在“流”的条件。焚风流在一个多世纪前首次被描述，当时假设了两种变暖效应的机制：一种是等熵下降机制，即来自高空的潜在暖空气被冷却下来，另一种是潜热加热和降水机制，即由于凝结和潜热释放，空气在上升时比在背风面干燥下降时冷却得更少。在这里，第一次，这些和其他焚风变暖机制的直接定量贡献。结果表明，需要一个新的范例后，它被证明是第三种机制，机械混合的焚风流的湍流，是显着的。事实上，根据流动动力学，三种变暖机制中的任何一种都可以占主导地位。一个新的拉格朗日热收支模型，后轨迹，高分辨率的数值模型输出，和飞机的观察。这项研究的重点是一个独特的自然实验室，一个允许明确量化的背风变暖，即南极半岛和拉森C冰架。这三种焚风变暖机制的重要性对山区的天气预报以及冰架融化和野火等相关危害具有影响。
The foehn effect is well known as the warming, drying, and cloud clearance experienced on the lee side of mountain ranges during "flow over" conditions. Foehn flows were first described more than a century ago when two mechanisms for this warming effect were postulated: an isentropic drawdown mechanism, where potentially warmer air from aloft is brought down adiabatically, and a latent heating and precipitation mechanism, where air cools less on ascent-owing to condensation and latent heat release-than on its dry descent on the lee side. Here, for the first time, the direct quantitative contribution of these and other foehn warming mechanisms is shown. The results suggest a new paradigm is required after it is demonstrated that a third mechanism, mechanical mixing of the foehn flow by turbulence, is significant. In fact, depending on the flow dynamics, any of the three warming mechanisms can dominate. A novel Lagrangian heat budget model, back trajectories, high-resolution numerical model output, and aircraft observations are all employed. The study focuses on a unique natural laboratory-one that allows unambiguous quantification of the leeside warming-namely, the Antarctic Peninsula and Larsen C Ice Shelf. The demonstration that three foehn warming mechanisms are important has ramifications for weather forecasting in mountainous areas and associated hazards such as ice shelf melt and wildfires.