Rossby waves

[Ari Epstein <awe@pimms.mit.edu>]

I've been asking around here (the MIT Physical Oceanography group),
and I believe I can add a little more information. 

Jim Green (Jim.Green@Snow.edu) forwarded:



>                  WEATHER-CHANGING OCEAN WAVES
>                    CHARTED FROM SPACE
>
> New results from the ocean-observing TOPEX/Poseidon
> satellite are challenging a fundamental oceanographic
> theory about the speed of large-scale ocean waves -- a
> finding that could ultimately revise science textbooks and
> improve global weather forecasting.
>
> The large-scale ocean waves, with wavelengths of hundreds
> of kilometers from one wave crest to the next, are called
> Rossby waves.  These waves carry a "memory" of weather
> changes that have happened at distant locations over the
> ocean, according to NSFfunded researcher Dudley Chelton of
> Oregon State University in Corvallis.
>
> Using data gathered by the satellite, scientists tracked
> the waves as they moved through the open ocean, and
> determined that, at mid-latitudes, the Rossby waves are
> moving two to three times faster than previously thought.
> Since Rossby waves can alter currents and corresponding
> sea surface temperatures, the waves influence the way the
> oceans release heat to the atmosphere and thus are able to
> affect weather patterns.  Says Chelton, "If the waves get
> from one side of the mid-latitude ocean to the other twice
> as fast, the ocean adjusts more rapidly to changes than we
> had previously thought."
>
> This more precise information about how fast the waves are
> traveling may help forecasters improve their ability to
> predict the effects of El Nino events on weather patterns
> years in advance.


The paper referred to here is "Global Observations of Oceanic Rossby
Waves," by Dudley B. Chelton and Michael G. Schlax, _Science_, 12
April 1996, Volume 272, pp. 234-238. The paper combines two very cool
topics: Rossby waves (a large-scale wave in which the "restoring
force" really comes from the conservation of angular momentum on a
spinning Earth [e-mail me if you'd like a more complete description;
Rossby waves are *not* the surface gravity wave that people typically
think of when they think about waves in the ocean]) and data from the
TOPEX/Poseidon satellite mission, which detects changes in sea-surface
height with an accuracy better than one centimeter. Rossby waves are
among the most important ways in which changes in oceanic and/or
atmospheric conditions can propagate for long distances, and the
TOPEX/Poseidon mission is one of the few tools available to
oceanographers who want to observe large areas of the ocean
simultaneously. 

What Chelton and Schlax report is that they have observed Rossby waves
travelling about twice as fast as linear theory predicts; their
observations are consistent with predictions made by certain numerical
models. The paper implies that the current theoretical understanding
of Rossby waves is incomplete in some very important ways, which could
have implications for a large number of oceanic and atmospheric
phenomena. 

I think I'll stop here for now, but if members of this list would like
more detailed information, please send me e-mail and I'll tell you
what I can.

Ari Epstein
awe@pimms.mit.edu