The winds and sea are in constant motion and their movements are closely interdependent. The wind not only generates waves, it also drives eddy movements on the ocean surface. For example, in the Eastern Mediterranean, northerly winds called the Etesians interact with the relief on the island of Crete. The peaks on land cause the wind to change course, thus generating swirling movements which the wind transfers to the sea to form what is known as the Ierapetra gyre. The strength of this gyre depends on the speed and direction of the wind.

Altimetry enables us to observe such phenomena, as it measures the peaks and valleys in the ocean surface around which eddies form (see last month's image: <link html applications circulation>A turbulent sea). Other spaceborne sensors such as the AVHRR, which measures sea-surface temperature, complement altimetry data.

See also:

• Applications: Ocean circulation and its variations
• Applications: Mediterranean Sea