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A whirlwind is a phenomenon in which a vortex of wind (a vertically oriented rotating column of air) forms due to instabilities and turbulence created by heating and flow (current) gradients. Whirlwinds can vary in size and last from a couple minutes to a couple hours. [1][2]
- Overview
- General features
- Dust devils
whirlwind, a small-diameter columnar vortex of rapidly swirling air. A broad spectrum of vortices occurs in the atmosphere, ranging in scale from small eddies that form in the lee of buildings and topographic features to fire storms, waterspouts, and tornadoes. While the term whirlwind can be applied to any atmospheric vortex, it is commonly restri...
At the centre of the whirlwind, atmospheric pressure is less than it is in the surrounding air, but the decrease is not large. Pressure drops of a few hectopascals (a few tenths of a pound per square inch) are typical in dust devils. (Standard atmospheric pressure at sea level is about 101 kilopascals, or 14.7 pounds per square inch.)
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The axis of rotation in a whirlwind is usually vertical, but it may be inclined. In small whirls, the direction of rotation may be either clockwise or counterclockwise. In larger whirls, outside forces may dictate that one direction of rotation dominates.
Perhaps the most ubiquitous whirlwind is the dust devil. It is likely that quite a few of these small vortices are present in the lowest several hundred metres of the atmosphere on many days, but only the rare ones that pick up detritus from the surface are seen. Certainly every summer, hundreds of thousands of dust devils form and travel across the arid and semiarid regions of the world. Observers report dust whirls almost daily during the hot season over the Sahara as well as the arid regions of Australia and the southwestern United States. They also are common over sections of India and the Middle East.
Dust devils occur most frequently under hot, clear-sky conditions with light winds. Such environments give rise to a strong heat flux from the hot surface of the Earth to the lowest layers of the atmosphere. This energy is absorbed by the atmosphere to produce a highly unstable layer near the ground. Release of the energy stored in this unstable layer leads to the formation of thermal plumes (large parcels of hot air rising from the surface). A dust devil draws on this stored energy to develop and then maintain itself. A light wind is required to start rotation in the rising plume. When dissipative forces, such as surface friction and eddy interaction with the environment, exceed the available energy, the whirlwind is destroyed.
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The stability of the surface layer of the atmosphere does not depend on its actual temperature, but on the rate of change of temperature with height in the layer. Any process that produces an unstable surface layer can give rise to thermal plumes and to whirlwinds. This accounts for the sighting of dust devils and related whirls under temperate conditions and even in cool conditions such as those of the subarctic. Dust devils have even been observed on Mars, where temperatures are much colder than on Earth.
This dependence on instability of the surface air layer is the reason dust devils are usually most active in the early afternoon, from 12:30 to 2:00 pm. During this period the heated ground surface attains its peak temperature and, therefore, the surface layer its greatest instability.
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Sep 21, 2018 · A whirlwind is defined as a vertical column of wind, or vortex, which is formed by sudden changes in atmospheric pressure. The energy produced by these winds enable them to pick up the debris of varying sizes, including snow, leaves, water, dust, and even fish. In extremely rare cases, whirlwinds formed near wildfires can pick up flames and ...
Whirlwind. Meteorological phenomenon From Wikipedia, the free encyclopedia. A whirlwind is a phenomenon in which a vortex of wind (a vertically oriented rotating column of air) forms due to instabilities and turbulence created by heating and flow (current) gradients. Whirlwinds can vary in size and last from a couple minutes to a couple hours.
Sep 25, 2023 · Whirwind Questions. Barbarian. Excalibur-22563 September 25, 2023, 11:51am 1. Hey guys, I am currently farming Travincal with a Whirlwind Barbarian and I need some help understanding how Whirlwind works. I’ve spend some time googling and messing with a calculator and I am still so confused. Long story short, is a dual setup better than of a 2 ...
A whirlwind. A dust devil at school ground. Whirlwind, 61 km northeast of Broome, Western Australia. A whirlwind is a vortex of wind (a straight rotating column of air) that forms because of turbulence created by heating and flow (current) differences. Whirlwinds happen all over the world and in any season.
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Base weapon speed shown in brackets is 10, it has an additional 40% increased attack speed. 10 - 40 = -30. So the IK maul hits the second to last whirlwind breakpoint, it needs 30% more ias to hit the last breakpoint, so if we put 2 sheals in it, or 2x 15 ias jewels, it hits max attacks per second with whirlwind.
