Oceanic eddies are distinct, closed cyclonic or anticyclonic circulations. Cyclonic eddies are generally cold core, while anticyclonic eddies are generally warm core. But if the temperature of the water increases as you move outward from the center of an eddy, the eddy is cold cored (coldest temperature at the center), regardless of the circulation. 

Eddies are formed in several different ways. They can develop when a meander in a major ocean current becomes very large and gets cut off from the main current. Such formations are similar to the cut-off highs and lows that occur

Figure 3-1-2.-Typical temperature profile across the Gulf Stream during spring.

in the primary circulation patterns found in the atmosphere. These eddies have diameters that range between tens of miles to hundreds of miles and, like the currents that form them, their circulations are strongest near the surface. Eddies are also produced by the deflection and/or channeling of an ocean current by the shape of the coastline and the topography of the ocean bottom. Small eddies (tens of miles in diameter)have also been observed to form from the intrusion of one water into another. The intruding water bends back towards itself, forming a small rapidly rotating eddy. 

The surface-temperature patterns of oceanic eddies are visible in infrared satellite imagery. The temperature differences across eddies produce gray-shade differences. Figure 3-1-4 shows eddies formed by meanders within the Gulf Stream.

Figure 3-1-3.An infrared picture showing shades of gray associated with thermal contrasts along the eastern coast of the United States.

Figure 3-1-4 .An enlarged view of a VHRR infrared picture showing anticyclonic eddies formed from shoreward meanders of the Gulf Stream.

Cold eddies are often partially encircled by a convective cloud line at their edge, while con-vective clouds may form directly over warm eddies.

Cold eddies act as an atmospheric stabilizer by cooling the air directly overhead, thereby slowing the movement of stronger winds aloft toward the surface. Thus, there is a tendency for the seas in cold eddies, and cold water in general, to be less rough than the surrounding warmer waters.

Eddies are also used tactically by submarines because of the sound propagation differences that exist inside and outside these circulations.

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