By Katy Hill, a BSc Marine Sciences graduate from SOC's School of Ocean and Earth Science (....now happily pursuing a MSc in Physical Oceanography with the Climate Modelling Group at the Univ. of Victoria, Canada)

Ocean temperature is very important in determining our climate. In Western Europe our climate would be much cooler if it wasnít for the Gulf Stream. On a global scale, the ocean acts like a central heating system, pumping tropically heated water to higher latitudes.

Satellite maps of sea surface temperature are powerful tools for studying processes at the ocean surface as they give us global coverage every few days. Recently it has become clear that these temperature readings are also useful for finding out about processes taking place below the surface.

Underneath the surface, water divides into different layers that are quite distinct and do not mix easily. Warmer water lies in a layer above much colder water - the interface between the two is called the thermocline. Rossby waves move along the thermocline. This movement, or propagation, can be seen on the surface by infra-red satellite sensors as a surface temperature signal.

This is useful when studying an area like the Southern Ocean that is notoriously difficult to survey. We have found Rossby waves that seem trapped in the Antarctic Circumpolar Current. Rossby waves propagate towards the west but with the eastward movement of the circumpolar current and the earthís rotation they seem to be moving eastwards or even appear to be stationary. Itís akin to trying to walk up a down escalator - unless you walk fast enough, the escalatorís speed wins and carries you backwards.

A feature that is attracting interest is a phenomenon named the Circumpolar Wave. This is a large-scale wave that travels at speeds of around 6 km a day, repeating every four to five years. Recent studies suggest that it can have a significant effect on the Southern Hemisphere's climate by altering patterns of ocean and wind circulation.

With highly accurate satellite instruments producing global sea surface temperature data, our understanding of the influence of ocean dynamics on our climate system is steadily improving.
 

(This short article has appeared on the issue 2 - Spring 2000 of OceanZone, the newsletters from SOC External affairs)
 

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