Low ocean-floor rises regulate subpolar sea surface temperature by forming baroclinic jets

H Mitsudera,T Wagawa,T Nakanowatari,T Nakamura,R Furue,H Nishigaki,S Ito,Y Fujii,T Miyama,H Nishikawa

doi:10.1038/s41467-018-03526-z

Abstract

Sea surface temperature (SST) fronts in mid- to high-latitude oceans have significant impacts on extratropical atmospheric circulations and climate. In the western subarctic Pacific, sharp SST fronts form between the cold subarctic water and the recently found quasi-stationary jets that advect warm waters originating in the Kuroshio northeastward. Here we present a new mechanism of the jet formation paying attention to the propagation of baroclinic Rossby waves that is deflected by eddy-driven barotropic flows over bottom rises, although their height is low (~500 m) compared with the depth of the North Pacific Ocean (~6000 m). Steered by the barotropic flows, Rossby waves bring a thicker upper layer from the subtropical gyre and a thinner upper layer from the subarctic gyre, thereby creating a thickness jump, hence a surface jet, where they converge. This study reveals an overlooked role of low-rise bottom topography in regulating SST anomalies in subpolar oceans.

Highlights

Sea surface temperature (SST) fronts in mid- to high-latitude oceans have significant impacts on extratropical atmospheric circulations and climate
Recent high-resolution satellite observations and numerical models have revealed that sea surface temperature (SST) variations associated with eddies and frontal jets in the mid- to high-latitude oceans can cause significant far-reaching influences on extra-tropical atmospheric circulations[1,2,3,4,5,6,7]
The SST front variability is evaluated by the empirical orthogonal function (EOF) of the latitude Φ(x, t) representing the maximum meridional SST gradient in the region 145°E −170°E, 35°N−47°N, where x, y, and t denote zonal coordinate, meridional coordinate, and time, respectively

Summary

Introduction

Sea surface temperature (SST) fronts in mid- to high-latitude oceans have significant impacts on extratropical atmospheric circulations and climate. In the western subarctic Pacific, sharp SST fronts form between the cold subarctic water and the recently found quasi-stationary jets that advect warm waters originating in the Kuroshio northeastward. Recent high-resolution satellite observations and numerical models have revealed that sea surface temperature (SST) variations associated with eddies and frontal jets in the mid- to high-latitude oceans can cause significant far-reaching influences on extra-tropical atmospheric circulations[1,2,3,4,5,6,7]. In the western North Pacific, SST variations are pronounced between 40°N and 43°N where SST gradients are large[4,8] This region is often referred to as the Subarctic Frontal Zone (SAFZ), which corresponds to the boundary between the subtropical and subarctic gyres[9,10]. This study reveals an overlooked role of small-amplitude bottom topography in the formation of surface jets and SST fronts in subpolar oceans

Methods

Results

Conclusion