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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Rossby number ： ウィキペディア英語版 Rossby number The Rossby number (Ro) named for Carl-Gustav Arvid Rossby, is a dimensionless number used in describing fluid flow. The Rossby number is the ratio of inertial to Coriolis force, terms $v\backslash cdot\backslash nabla\; v\backslash sim\; U^2\; /\; L$ and $\backslash Omega\backslash times\; v\backslash sim\; U\backslash Omega$ in the Navier–Stokes equations, respectively. It is commonly used in geophysical phenomena in the oceans and atmosphere, where it characterizes the importance of Coriolis accelerations arising from planetary rotation. It is also known as the Kibel number. The Rossby number (Ro and not Ro) is defined as: :$\backslash mathrm=\backslash frac$ where ''U'' and ''L'' are, respectively, characteristic velocity and length scales of the phenomenon and ''f'' = 2 Ω sin φ is the Coriolis frequency, where Ω is the angular frequency of planetary rotation and φ the latitude. A small Rossby number signifies a system which is strongly affected by Coriolis forces, and a large Rossby number signifies a system in which inertial and centrifugal forces dominate. For example, in tornadoes, the Rossby number is large (≈ 103), in low-pressure systems it is low (≈ 0.1 – 1) and in oceanic systems it is of the order of unity, but depending on the phenomena can range over several orders of magnitude (≈ 10−2 – 102). As a result, in tornadoes the Coriolis force is negligible, and balance is between pressure and centrifugal forces (called ''cyclostrophic balance'').〔 Cyclostrophic balance also commonly occurs in the inner core of a tropical cyclone. In low-pressure systems, centrifugal force is negligible and balance is between Coriolis and pressure forces (called ''geostrophic balance''). In the oceans all three forces are comparable (called ''cyclogeostrophic balance''). For a figure showing spatial and temporal scales of motions in the atmosphere and oceans, see Kantha and Clayson. When the Rossby number is large (either because ''f'' is small, such as in the tropics and at lower latitudes; or because ''L'' is small, that is, for small-scale motions such as flow in a bathtub; or for large speeds), the effects of planetary rotation are unimportant and can be neglected. When the Rossby number is small, then the effects of planetary rotation are large and the net acceleration is comparably small allowing the use of the geostrophic approximation. == See also == * Coriolis effect * Centrifugal force 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Rossby number」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.