A two‐layer diagnostic model of the long‐term physical evolution of warm‐core ring 82B

Shipboard data from cruises in the 1982 time series on a single Gulf Stream warm-core ring are composited in a cylindrical coordinate system following the motion of the ring. Measurements of 10°C isotherm depth are used with a two-layer model of the ring's structure to compute gradient current, kinetic energy, available potential energy (APE), and potential vorticity in the ring, The momentumrelated quantities are compared with surface-derived velocity measurements by using an acoustic Doppler log (APOC; Joyce and Kennelly, this issue). The volume of waters carried with the ring are also computed on the basis of thermal data. The changes in these quantities as the ring evolves are discussed. The evolution of the ring can be divided into two periods. The first, from April to late June, while the ring is isolated from strong interactions with the Gulf Stream, is associated with slow changes in ring properties. During this period, the ring loses APE at a rate of 94×106 W (94 MW). Kinetic energy is constant within the measurement errors. Ring volume for waters warmer than 10°C decreases at 0.04×106 m3 s−1 (0.04 Sv). A shift in ring volume out to larger radius is observed. After this interval the ring is involved in several interactions with the Gulf Stream and topography. Ring energy is lost at rates exceeding 900 MW. The ring volume is diminished at 1.4 Sv during the July period. Within the measurement errors, however, the potential vorticity at the center of the ring is conserved from April through August, implying nearly inviscid dynamics.

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