Impact of oceanic-scale interactions on the seasonal modulation of ocean dynamics by the atmosphere

TLDR

Ocean eddies, which account for about 80 % of ocean kinetic energy, are traditionally attributed to large‑scale internal instabilities between upper and interior layers, but recent work highlights the significant contribution of smaller 1–50 km structures and suggests their role may influence climate dynamics and future satellite observations. The study aims to demonstrate that ocean eddies are sustained by small‑scale mixed‑layer instabilities driven by large‑scale winter atmospheric forcing, rather than by large‑scale internal instabilities. Using a high‑resolution simulation of the realistic North Pacific Ocean, the authors model small‑scale mixed‑layer instabilities triggered by large‑scale winter atmospheric forcing. The model shows that eddy kinetic energy varies seasonally across much of the North Pacific, with amplitude changes approaching a factor of two.

Abstract

Abstract Ocean eddies (with a size of 100–300 km), ubiquitous in satellite observations, are known to represent about 80% of the total ocean kinetic energy. Recent studies have pointed out the unexpected role of smaller oceanic structures (with 1–50 km scales) in generating and sustaining these eddies. The interpretation proposed so far invokes the internal instability resulting from the large-scale interaction between upper and interior oceanic layers. Here we show, using a new high-resolution simulation of the realistic North Pacific Ocean, that ocean eddies are instead sustained by a different process that involves small-scale mixed-layer instabilities set up by large-scale atmospheric forcing in winter. This leads to a seasonal evolution of the eddy kinetic energy in a very large part of this ocean, with an amplitude varying by a factor almost equal to 2. Perspectives in terms of the impacts on climate dynamics and future satellite observational systems are briefly discussed.