The Potential Vorticity Structure of Equatorial Deep Jets

Abstract

The equatorial deep jets are often modeled as equatorially trapped long waves, either Kelvin or Rossby. Rossby waves perturb potential vorticity but Kelvin waves do not; therefore the potential vorticity structure of a 16-month mean velocity section from 3°N to 3°S on 159°W is examined. To distinguish the equatorial deep jets from flow components with larger vertical scales, the mean profiles were decomposed into a low-vertical-mode component and a residual, dominated by the deep jets. The deep jets resemble a first-meridional-mode Rossby wave; their velocity at 2°N and 2°S is opposite in direction to their velocity on the equator, and consequently they show a potential vorticity perturbation. The zero crossings of the jets zonal velocity are at 1°30?N and S, farther from the equator than the 1°N and S predicted by linear wave theory. One possible explanation for this broadening is meridional advection of the jets by higher-frequency motions such as Rossby?gravity waves.