The dissipation of kinetic energy in a warm‐core ring

Abstract

Profiles of the rate of viscous dissipation of kinetic energy in a Gulf Stream warm‐core ring show large rates in the thermocline and in the entrainment region near the edge of the ring. The thermostad has very low levels of dissipation except where that region is in contact with the Gulf Stream. Dissipation rates in the thermocline are independent of the large scale vertical shear and are consistent with the concept of near‐inertial wave trapping by the ring's geostrophic shear. Near the edge, to depths of 1000 m, turbulence is associated with entrainment and interleaving. The e‐fold decay scale for the dissipation of the ring's total energy is 2 to 3 years, but is only 140 days for the kinetic energy, so energy conversion from potential to kinetic must be occurring on time scales of 10 to 30 days. The vertical eddy diffusivity of the ring is 0.1 × 10−4 m2/s except in the thermostad where it is smaller by approximately a factor of 10. The eddy viscosity is more than 10 × 10−4 m2/s; hence tubulent diffusion is relaxing the velocity field faster than the thermal field.