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