Rossby waves detected in global ocean colour data

We demonstrate for the first time the detectability of mid-latitude Rossby waves in global ocean colour data from the Japanese Ocean Colour and Temperature Scanner (OCTS) and U.S. Sea-viewing Wide Field-of-view Sensor (SeaWiFS) radiometers. By producing longitude-time plots of the merged OCTS and SeaWiFS datasets we observe at some latitudes westward propagating signals. Their signature is much weaker than the annual phytoplankton cycle but can be highlighted by filtering the plots. The main propagating speed is estimated with the Radon Transform and increases equatorward, as expected for Rossby waves. A comparison with both speeds derived from altimeter data and the zonal mean of the speed predicted by a recent theory of Rossby wave propagation shows a broad agreement. We conclude that Rossby waves are sometimes observable in the ocean colour field and thus have some effects on biology, and we suggest two simple hypotheses for the underlying interaction mechanism.