Planetary waves in the oceans:a look from space

Planetary waves in the oceans are both important (for ocean circulation) and fascinating. One of their fascinating aspects is that the definitive proof of their existence and ubiquity (predicted by Carl-Gustav Rossby\'s in the late 1930s) has been obtained only recently, thanks to the advent of accurate altimetric measurements from satellites. Another very intriguing aspect is that planetary waves are now being seen in almost any satellite dataset that we look at: not only sea surface height, but also sea surface temperature (for instance from ATSR) and ocean colour.
The signature of planetary waves in ocean colour implies some effects of the waves on biology and raises interesting questions on the underlying mechanisms: is that signature purely an effect of horizontal advection or could it be the result of vertical motion? In this talk I will first describe some of the techniques that we use to observe planetary waves in satellite data (Altimetry and SST), and I will compare the results with the theoretical predictions. These include some techniques for the tracking of individual wave events that have been developed within the EU-funded SOFT Project. Then I will present and a modelling and observational study where we have compared the signature of the waves in the SSH and ocean colour datasets and tested several mechanisms for production of the signal, including horizontal (passive) north-south advection by the wave against a mean background gradient, and vertical upwelling of nitrate, which is converted into chlorophyll. The results show that over most of the ocean, the chlorophyll signal is well explained by horizontal advective processes, although we cannot rule out that there exist locations where the biological (vertical) mechanisms may be playing a significant role.