vorticity

Vorticity is a measure of rotation in the atmosphere, or “spin,” in the air. If the spin, as viewed from above, is counterclockwise in the Northern Hemisphere, it is called a vorticity cyclonic and given a positive value. If the spin is clockwise, it is called a vorticity anticyclonic and given a negative value. The opposite conventions apply in the Southern Hemisphere. In forecasting large-scale weather events, one is concerned primarily with “relative vorticity” and focuses on the rotation of air around a vertical axis, much like the rotation of a hurricane over the earth’s surface. The vorticity caused by the Coriolis effect is another matter. Consider a large volume of air rotating around a common center just as a very large wheel would spin around its axis. One component of the relative vorticity is due to its pure rotation. The greater the wind speed, or V, in this circular motion and the smaller the radius of rotation, R, the greater the vorticity. The contribution toward relative vorticity from rotation alone is V/R. Because tornadoes have high wind speeds and nominal radii of only hundreds of meters, the vorticity associated with them is very high. Hurricanes have high winds, too, but the radius of rotation is greater, so their relative vorticity is less than for tornadoes. A second source of relative vorticity arises from wind shear, which can be defined as a change in wind speed between two locations. Wind shear in the horizontal imparts a spin to volumes of air caught in the flow. This shear gives rise to cyclonic vorticity because it imparts a counterclockwise spin to volumes of air caught in the flow. There is a good correlation between large values of vorticity and centers of low pressure in the atmosphere. The association of low pressure and high vorticity with foul weather is a generalization that is quite often true.

Aviation dictionary. 2014.

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  • Vorticity — is a mathematical concept used in fluid dynamics. It can be related to the amount of circulation or rotation (or more strictly, the local angular rate of rotation) in a fluid.Clancy, L.J., Aerodynamics , Section 7.11] The average vorticity zeta… …   Wikipedia

  • Vorticity — Dieser Artikel oder Abschnitt bedarf einer Überarbeitung. Näheres ist auf der Diskussionsseite angegeben. Hilf mit, ihn zu verbessern, und entferne anschließend diese Markierung. Vorticity (auch Wirbelstärke oder Vortizität genannt) stellt eine… …   Deutsch Wikipedia

  • vorticity — vortex ► NOUN (pl. vortexes or vortices) ▪ a whirling mass, especially a whirlpool or whirlwind. DERIVATIVES vortical adjective vorticity noun. ORIGIN Latin, eddy …   English terms dictionary

  • vorticity — noun Date: 1888 1. the state of a fluid in vortical motion; broadly vortical motion 2. a measure of vortical motion; especially a vector measure of local rotation in a fluid flow …   New Collegiate Dictionary

  • vorticity — /vawr tis i tee/, n., pl. vorticities. Mech. a measure of the circulation of a fluid: a quantity equal to twice the angular momentum of a particle of the fluid around which there is circulation. [1890 95; < L vortic (s. of vortex; see VORTEX) +… …   Universalium

  • vorticity — noun A property of a fluid related to local angular rotation …   Wiktionary

  • vorticity — vor·tic·i·ty …   English syllables

  • vorticity — vȯ(r)ˈtisəd.ē noun ( es) Etymology: Latin voltic , vortex + English ity 1. : the state of a fluid in vortical motion 2. : twice the angular velocity of a small element of fluid around which there is circulation …   Useful english dictionary

  • Vorticity equation — The vorticity equation is an important prognostic equation in the atmospheric sciences. Vorticity is a vector, therefore, there are three components. The equation of vorticity (three components in the canonical form) describes the total… …   Wikipedia

  • vorticity flux density — sūkurinio srauto tankis statusas T sritis fizika atitikmenys: angl. vortex flux density; vorticity flux density vok. Wirbelflußdichte, f rus. плотность вихревого потока, f pranc. densité de flux tourbillonnaire, f …   Fizikos terminų žodynas

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