Azimuthal structure of a cyclonic Gulf Stream ring

Abstract

During the period June 8–19, 1979, an intensive expendable bathythermograph survey of a Gulf Stream ring was made. After mapping the irregularly spaced data onto a regular grid, and azimuthally decomposing the temperature field at constant depth into Fourier constituents einθ, we find the n = 2 mode to be the dominant one. We calculate the geostrophic stream function utilizing the hydrostatic equation and the measured temperature/salinity curves. The stream function is expressed in cylindrical polar coordinates (r, θ, z) and decomposed into a steady, azimuthally independent part ψ(r, z) and a temporally varying disturbance part ϕ(r, θ, z, t) with azimuthal dependence. The quasi‐geostrophic energy equation for ϕ contains source terms representing the interaction of the ψ and ϕ fields by baroclinic and barotropic processes. We find that ∼90% of the total disturbance energy flux results from baroclinic processes, and the remainder from the barotropic exchanges. The time scale of this energy flux into the disturbance ϕ is of the order of 16 days, while the time scale of an energy loss from the disturbance is ∼4.5 days.