|During an average year 10 to 15 rings are formed. The rings are usually between 150-300 km in diameter, and can have rotational velocities over 1 m/s. The rings generally drift to the southwest at approximately 5 km/day. Warm core rings are always located between the Gulf Stream and the continental slope. The life cycle of a warm core ring is generally a few months to a year. These rings usually are reabsorbed by the Gulf Stream, although they also can break apart if they move onto the continental shelf. Warm core rings travel to the west, so many warm core rings are reabsorbed into the Gulf Stream near Cape Hatteras as they are squeezed between the Gulf Stream and the continental shelf. This process of rings being reabsorbed back into the Gulf Stream is known as coalescence.|
|Warm core rings are easily observed in satellite images due to the large thermal contrast between the ring and the cold surrounding waters.
For example, on the image to the right, a warm core ring is approaching Cape Hatteras and will soon be absorbed in the Gulf Stream. Further east another ring is easily visible.
|Cold Core rings also are reabsorbed into the Gulf Stream, but they may have life cycles of several years since they may drift far into the Sargasso Sea before eventually drifting near the Gulf Stream again. Cold core rings often lose their identity on satellite images due to the intense heating of the surface waters south of the Gulf Stream. Since the satellite can only measure the surface temperature, these cold rings often become masked by the warm surface layer. Cold core rings are the ocean's equivalent to an atmospheric low pressure system and, thus, are often referred to as cyclonic eddies. Gulf Stream rings often exhibit large vertical structure and may extend several kilometers deep. Cold core rings are characterized by a "doming" toward the surface of the deep isotherms, while a warm core ring results in a deepening of the isotherms.|
|This doming of the isotherms is shown below in an actual transect across the Gulf Stream. A cold core ring is located approximately 100 km to the south of the Gulf Stream. For example, the 16°C isotherm (the isotherm separating the pink and blue in the figure) undergoes a 600m vertical excursion in the cold core ring. Across a ring and across the Gulf Stream the sea surface also slopes. The sea surface slope is always opposite the isotherm slope. The sea surface slope across the Gulf Stream is approximately one meter.|