Detection of Rossby waves in ocean colour data

This paper deals with some observations of the signature of mid-latitude planetary waves (Rossby waves) in global chlorophyll-a data from the Ocean Colour and Temperature Scanner (OCTS) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). By producing longitude-time plots of the merged OCTS and SeaWiFS monthly composites the authors detect, at some latitudes, westward propagating signals whose characteristics are consistent with those expected for long-wavelength baroclinic Rossby waves. The propagating signals are superimposed on the much stronger annual phytoplankton cycle, however their detection may be enhanced by band-pass filtering the longitude-time plots. The propagation speed depends on latitude, with speed increasing equatorward, as expected for Rossby waves. The authors show an initial comparison of the results with those obtained from sea surface height data. Finally, they discuss possible explanations for the phenomenon