# Atmospheric eddies, waves etc: definitions

1. ### jf22901

55
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?

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3. ### JesseC

282
It is difficult to know without reading the texts, could you link the websites and books? When I was learning about this the lecturer often talked about waves and eddies interchangeably. The latter is often caused by instabilities in the former. One thing that you could do is check the mathematics for consistency. When considering meridional transport, eddies are characterised by quantities that vary in time and stationary eddies by quantities that vary zonally but not in time.

2
the definition i know about is

$$v = <\bar{v}>+<v> + v'$$ where $$<\cdot>$$ is time averaging, and $$\bar{\cdot}$$ is zonal averaging. The terms of the RHS are, respectively, the mean meridional velocity, the stationary eddies, and the transient eddies.

When people talk about "stationary/traveling waves" I thought they were typically talking about Rossby waves/kelvin waves/etc.

5. ### olivermsun

933
In a general sense, waves are typically the motions which have a well-defined dispersion relation, e.g., Rossby waves. In the framework you're talking about, the "stationary" Rossby/planetary waves are important because they're associated with fixed topographic features (the big mountain ranges), so they "survive" even after time-averaging. The eddies on the other hand have some transient zonal structure which supposedly averages to zero (if you average both in time and in the zonal direction).