A Persistent Deep Anticyclonic Vortex in the Rockall Trough Sustained by Anticyclonic Vortices Shed From the Slope Current and Wintertime Convection

Angelina Smilenova,Mathieu Le Corre,Loïc Houpert,Yves Reecht,Jonathan Gula

doi:10.1029/2019jc015905

Abstract

AbstractThe presence of a persistent surface anticyclone centered at approximately 55°N, 12°W in the Rockall Trough, northeast North Atlantic, has been previously noted in satellite altimetry data. Here, we show that this surface anticyclone is the imprint of a deep, persistent, non‐stationary anticyclonic vortex. Using wintertime 2007 and 2011 ship‐board data, we describe the anticyclone's vertical structure for the first time and find that the anticyclone core is partly made of warm and salty Mediterranean Overflow Water. The anticyclone has a radius of ~40 km, it stretches down to 2,000 m, with a velocity maximum around 500 m. To analyze the anticyclone's generating mechanism, we use a mesoscale‐resolving (~2 km) simulation, which produces a realistic pattern of the Rockall Trough anticyclone. The simulation indicates that the anticyclone is locally formed and sustained by two types of processes: wintertime convection and merger with anticyclonic vortices shed from the slope current flowing poleward along the eastern Rockall Trough slope. Intense negative vorticity filaments are generated along the Rockall Trough south‐eastern slope, and they encapsulate Mediterranean Overflow Water as they detach and grow into anticyclonic vortices. These Mediterranean Overflow Water‐rich vortices are advected into the trough, consequently merging with the Rockall Trough anticyclone and sustaining it. We suggest that the Rockall Trough anticyclone impacts regional intermediate water masses modifications, heat and salt budgets locally, and further afield into the neighboring subpolar northeast North Atlantic.

Highlights

Eddies at the mesoscale (Chelton et al, 2007) and the submesoscale (McWilliams, 1985) populate the ocean
Ship‐ board, and model data, we show that the altimetry‐defined anticyclone is an imprint of a subsurface‐intensified anticyclonic vortex, the Rockall Trough (RT) anticyclone, and highlight its vertical structure and formation mechanism
The ship‐board and model data show that the RT anticyclone is a deep vortex, its core delimited by the 27.3–27.7 kg m−3 isopycnals, stretching within the ~600/650

Summary

Introduction

Eddies at the mesoscale (Chelton et al, 2007) and the submesoscale (McWilliams, 1985) populate the ocean. (Sub)mesoscale eddies are three‐dimensional oceanic structures, found at various depths within the water column (e.g., Bosse et al, 2016; Ebbesmeyer et al, 1986). They are common in SMILENOVA ET AL. Depending on the depth of intensification, eddies are categorized as surface‐intensified or subsurface‐intensified (Assassi et al, 2016). Their generating mechanisms range from large‐scale currents instabilities to small‐scale turbulence or deep convection events (e.g., Carton, 2001; McWilliams, 1985). Eddies can extract or provide momentum and energy to the large‐scale mean currents, modifying the overall large‐scale ocean circulation (e.g., Le Corre et al, 2020; Lozier, 1997; Morrow & Birol, 2004)

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