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uk.sci.weather (UK Weather) (uk.sci.weather) For the discussion of daily weather events, chiefly affecting the UK and adjacent parts of Europe, both past and predicted. The discussion is open to all, but contributions on a practical scientific level are encouraged. |
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On May 6, 1:03*am, Liam Steele wrote:
On 05/05/13 23:50, Len Wood wrote: On May 5, 8:20 pm, Liam Steele wrote: Hi all. I'm reading up on types of atmospheric motion, and when discussing the meridional transport of various properties the motion is generally split into three components: 1. Mean meridional circulation 2. Transient eddies 3. Stationary waves However, depending on what book, article or website I read, I come across the terms transient eddies, stationary eddies, travelling waves, stationary waves and non-travelling waves. Is this just a case of different terminology for the same thing, or are there specific differences? Are transient eddies and travelling waves the same? Are stationary eddies, stationary waves and non-travelling waves the same? Thanks in advance! -- Liam Depends a bit on scale. Transient eddies usually refer to things like mid-latitude depressions. Sometimes called baroclinic eddies. These are embedded in larger planetary scale waves which may or may not be stationary. Rossby waves (barotropic waves) are planetary scale waves which derive from the variation of the Coriolis parameter with latitude. You could average out the transient eddies (noise) over a long enough period to just leave the Rossby waves. But the hemispheric flow you see at a given instant depends on feedback across all scales. Len Wembury Thanks Len, that's a great help. I'm happy with my understanding of transient eddies, but I'm still not sure about stationary eddies/stationary waves. I can see how a Rossby wave which is deflected due to topography or some other reason can lead to a stationary eddy (blocking high?). But is a meandering planetary wave the only method of forming a stationary eddy? -- Liam Milton Keynes There are occasions when the wave pattern becomes stationary. These times are associated with the wave speed (phase speed) of the waves. This is always westward (negative). It increases as the wavelength increases. But, mean tropospheric flow is eastwards. So the Rossby waves will move east or west depending on the relative magnitude of phase speed c and zonal wind speed u. The planetary scale Rossby wave will appear stationary when u is about the same magnitude as c. So you can see that the stationary nature of the large waves is dependent on a number of things. The highly variable zonal (westerly) wind for a start. Len Wembury |
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