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wadiIn regions of the Middle East and North Africa, a stream bed or channel that only carries water during the rainy season. In the southwest United States, the equivalent terms would be arroyo or wash.
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wake low1. (Or wake depression.) In meteorology, a surface low pressure area or mesolow (or the envelope of several low pressure areas) to the rear of a squall line; most commonly found in squall lines with trailing stratiform precipitation regions, in which case the axis of the low is positioned near the back edge of the stratiform rain area. 2. (Or wake depression.) In fluid dynamics, a low pressure area on the downstream side of an object embedded in a flow.
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wake turbulenceA disruption of airflow caused by the passage of a body through the air. In aviation, wake turbulence has been known to cause upset of one aircraft following another. The Federal Aviation Administration has issued regulations requiring aircraft to take off, land, and fly minimum distances behind other aircraft. These distances vary by aircraft type.
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wakeThe region of turbulence immediately to the rear of a solid body in motion relative to a fluid. Under certain conditions a series of vortices may form in the wake and extend downstream; such a vortex train in a turbulent wake is called a vortex street. Compare lee eddies.
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waldsterbenGerman expression (literally, “forest death”) for the forest dieback or decline usually associated with the effects of acid rain.
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Walker circulationA direct cell oriented along the equator; originally used by Bjerknes (1969) to refer to the cell induced by the contrast between the warm waters of the western Pacific and the cooler waters of the eastern Pacific. Variability in this cell is associated with the Southern Oscillation. The term is now sometimes used to refer to the entire chain of east–west equatorial circulation cells that stretches around the globe.
Bjerknes, J., 1969: Tellus, 18, 820–829.
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wall cloud(Sometimes referred to as pedestal cloud.) A local, often abrupt lowering from a cumulonimbus cloud base into a low-hanging accessory cloud, normally a kilometer or more in diameter. A wall cloud marks the lower portion of a very strong updraft, usually associated with a supercell or severe multicell storm. It typically develops near the precipitation region of the cumulonimbus. Wall clouds that exhibit significant rotation and vertical motions often precede tornado formation by a few minutes to an hour.
Fujita, T., 1959: A detailed analysis of the Fargo tornadoes of June 20, 1957. U.S. Wea. Bur. Res. Paper 42, p.15.
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