Talk:Rossby parameter

Equation Change[edit]

Per the following discussion posted at WP:RD/S (May 24, 2007):

More atmospheric physics for you! Our article on Rossby waves says that the wave speed is given by

c=u-{\frac {\beta }{k^{2}+l^{2}}}

where c is the wave speed, u is the mean westerly flow, $\beta$ is the Rossby parameter, and k and l are the longitudinal and latitudinal wavenumbers. The Rossby parameter is given as

\beta ={\frac {2\omega cos\phi }{a}}

where $\phi$ is the latitude, $\omega$ is the angular speed of the Earth's rotation, and a is the mean radius of the Earth.

Given the above, I cannot see how c is anything other than tiny. Yet it is not.

For example, if I put in u = 3, k = 5, l = 3 and calculate $\omega$ for a latitude of 60 degrees, I get an answer of order $10^{-13}$ , which is far too small.

I am surely misunderstanding something. Can someone check through this and see where I am going wrong? Many thanks, →Ollie (talk • contribs) 01:22, 24 May 2007 (UTC)[reply]

I agree with your assessment. Something must be awry! My understanding of the units in the problem suggest that

\beta

must be in units of velocity (meters/sec). However, because it is defined as

\omega /a=sec^{-1}/meters

, this does not work out. So, perhaps it ought to be defined as:

\beta =2a\omega cos\phi

This would make beta quite a bit larger (~10¹²x, which solves our issue quite nicely). I will try to find an alternative source for this equation which may verify my belief. Nimur 15:08, 24 May 2007 (UTC)[reply]

This lecture note seems to corroborate my belief that earth-radius should be multiplied, not divided. I will edit the articles in question. Nimur 15:16, 24 May 2007 (UTC)[reply]

End of copied discussion

Please discuss any issues below this line. Nimur 15:21, 24 May 2007 (UTC)[reply]

Yes, the radius a should be in the denominator, as traditionally defined. You can verify here:

http://amsglossary.allenpress.com/glossary/search?id=rossby-parameter1

Or any GFD texts would tell you the same thing.

Pkamostai (talk) 13:23, 20 December 2007 (UTC)[reply]

Equation[edit]

Is the current expression of the Rossby parameter really correct? The above equation

c=u-{\frac {\beta }{k^{2}+l^{2}}}

suggests $\beta$ has a dimension $[m^{-1}s^{-1}]$ , since dimension of $k$ is $[m^{-1}]$ and $c$ 's is $[ms^{-1}]$ . So the previous equation

\beta ={\frac {2\omega cos\phi }{a}}

seems correct to me.

Am I missing something? 210.174.33.192 19:12, 13 November 2007 (UTC)[reply]

Yes, the radius a should be in the denominator, as traditionally defined. You can verify here: http://amsglossary.allenpress.com/glossary/search?id=rossby-parameter1 Or any GFD texts would tell you the same thing. —Preceding unsigned comment added by Pkamostai (talk • contribs) 13:21, 20 December 2007 (UTC)[reply]

This was the source of confusion some time ago (see the above discussion). I will defer to your more recent edits since I'm not an expert in the field... Nimur (talk) 06:36, 22 December 2007 (UTC)[reply]

No φ in the equation?[edit]

I'm missing something too. The text says φ represents latitude, but there is not φ in the formula. Or am I just going blind? // Jontew (talk) 13:29, 26 November 2010 (UTC)[reply]

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