The effect of upper ocean eddies on the non‐steric contribution to the barotropic mode

Abstract

The non‐steric contribution to sea surface height (SSH) variability hampers the use of satellite altimeter data in mapping steric‐related variability. Here, two eddy‐resolving 1/16° world ocean simulations are used to investigate the effects of mesoscale flow instabilities on the non‐steric (or abyssal ocean) contribution to the global barotropic mode. Model results show the non‐steric component accounting for >50% of the total SSH variability over 37% of the world ocean in the model, predominantly at mid and high latitudes. Most of this is either wind‐driven and deterministic or eddy‐driven and nondeterministic. Upper ocean flow instabilities drive deep flows and generate non‐steric SSH variability maxima (5–10 cm rms or more) in many major current systems throughout the world ocean. Resulting ocean anomalies are a nondeterministic response to atmospheric forcing and an eddy‐resolving data‐assimilative ocean model that demonstrates the essential dynamics is needed to depict their evolution.