How satellites have improved our knowledge of planetary waves in the oceans
Paolo Cipollini(1) , Peter G. Challenor(1) , David Cromwell(1) , Ian S. Robinson(1) , and Graham D. Quartly(1)
National Oceanography Centre, Southampton,
SO14 3ZH Southampton,
In this paper we describe the contribution that Earth Observation techniques in general, and 15 years of altimetry in particular, have brought to our knowledge of extra-tropical planetary waves in the ocean, both baroclinic and barotropic.
Early observations with Geosat data showed the presence of a clear baroclinic wave signature in the SSH record; their ubiquity was subsequently demonstrated with the Topex/Poseidon and ERS datasets. These global observations highlighted significantly faster waves with respect to the classical theory of planetary wave propagation, calling for a revision of the theory. In this paper we first review a number of satellite-based studies showing planetary waves and contrast them with the many improvements in the theory that they have triggered, showing how altimetric as well as SST-based observations of planetary waves have contributed significantly to elucidate this aspect of ocean dynamics Then we illustrate the changes of amplitude of the planetary wave signal in the global ocean, and discuss some hypothesis for the presence of distinct ‘waveguides’ of enhanced wave activity. We also discuss a number of spectral and statistical techniques that allow an evaluation of the wave features (including their non-zonal characteristics), and the resulting prospects for planetary wave forecast.
Finally, we review the progress in the observation of barotropic waves, which is close to the limit of the sampling capability of the present altimeters’ constellation, but nevertheless has been successfully attempted, at least in some cases.