The Causes of Foehn Warming in the Lee of Mountains

Elvidge, Andrew D. and Renfrew, Ian A. (2016) The Causes of Foehn Warming in the Lee of Mountains. Bulletin of the American Meteorological Society, 93 (7). pp. 455-466. ISSN 0003-0007

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Abstract

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.

Item Type: Article
Additional Information: This article is licensed under a Creative Commons Attribution 4.0 license.
Faculty \ School: Faculty of Science > School of Environmental Sciences
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Depositing User: Pure Connector
Date Deposited: 11 Oct 2016 10:00
Last Modified: 22 Jul 2020 00:06
URI: https://ueaeprints.uea.ac.uk/id/eprint/60838
DOI: 10.1175/BAMS-D-14-00194.1

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