Orographic Precipitation in the Tropics: The Dominica Experiment

Ronald B. Smith Department of Geology and Geophysics, Yale University, New Haven, Connecticut

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Justin R. Minder Department of Geology and Geophysics, Yale University, New Haven, Connecticut

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Alison D. Nugent Department of Geology and Geophysics, Yale University, New Haven, Connecticut

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Trude Storelvmo Department of Geology and Geophysics, Yale University, New Haven, Connecticut

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Daniel J. Kirshbaum Department of Atmospheric and Oceanic Sciences, McGill University, Montreal, Quebec, Canada

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Robert Warren Department of Meteorology, University of Reading, Reading, United Kingdom

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Neil Lareau Department of Atmospheric Sciences, University of Utah, Salt Lake City, Utah

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Philippe Palany Météo-France, Martinique

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Arlington James Forestry Division, Dominica

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Jeffrey French Department of Atmospheric Science, University of Wyoming, Laramie, Wyoming

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The Dominica Experiment (DOMEX) took place in the eastern Caribbean from 4 April to 10 May 2011 with 21 research flights of the Wyoming King Air and several other observing systems. The goal was an improved understanding of the physics of convective orographic precipitation in the tropics. Two types of convection were found. During a period of weak trade winds, diurnal thermal convection was seen over Dominica. This convection caused little precipitation but carried aloft air with island-derived aerosol and depleted CO2. During periods of strong trades, mechanically forced convection over the windward slopes brought heavy rain to the high terrain. This convection was “seeded” by trade-wind cumuli or neutrally buoyant cool wet patches of air. In this mechanically forced convection, air parcels did not touch the island surface to gain buoyancy so no island-derived tracers were lofted. With fewer aerosols, the mean cloud droplet diameter increased from 15 to 25 μm. Plunging airflow and a wake were found in the lee of Dominica. The DOMEX dataset will advance our understanding and test our theories of cumulus triggering and aerosol influence on precipitation.

CORRESPONDING AUTHOR: Professor Ronald B. Smith, Dept. of Geology and Geophysics, Yale University, P.O. Box 208109, New Haven, CT 06520-8109, E-mail: ronald.smith@yale.edu

A supplement to this article is available online (10.1175/BAMS-D-11-00194.2)

The Dominica Experiment (DOMEX) took place in the eastern Caribbean from 4 April to 10 May 2011 with 21 research flights of the Wyoming King Air and several other observing systems. The goal was an improved understanding of the physics of convective orographic precipitation in the tropics. Two types of convection were found. During a period of weak trade winds, diurnal thermal convection was seen over Dominica. This convection caused little precipitation but carried aloft air with island-derived aerosol and depleted CO2. During periods of strong trades, mechanically forced convection over the windward slopes brought heavy rain to the high terrain. This convection was “seeded” by trade-wind cumuli or neutrally buoyant cool wet patches of air. In this mechanically forced convection, air parcels did not touch the island surface to gain buoyancy so no island-derived tracers were lofted. With fewer aerosols, the mean cloud droplet diameter increased from 15 to 25 μm. Plunging airflow and a wake were found in the lee of Dominica. The DOMEX dataset will advance our understanding and test our theories of cumulus triggering and aerosol influence on precipitation.

CORRESPONDING AUTHOR: Professor Ronald B. Smith, Dept. of Geology and Geophysics, Yale University, P.O. Box 208109, New Haven, CT 06520-8109, E-mail: ronald.smith@yale.edu

A supplement to this article is available online (10.1175/BAMS-D-11-00194.2)

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