Preprints
https://doi.org/10.5194/os-2021-10
https://doi.org/10.5194/os-2021-10

  15 Feb 2021

15 Feb 2021

Review status: a revised version of this preprint was accepted for the journal OS and is expected to appear here in due course.

A dynamically based method for estimating the Atlantic overturning circulation at 26° N from satellite altimetry

Alejandra Sanchez-Franks, Eleanor Frajka-Williams, Ben I. Moat, and David A. Smeed Alejandra Sanchez-Franks et al.
  • National Oceanography Centre, University of Southampton Waterfront Campus, European Way, Southampton, SO14 3ZH, UK

Abstract. The large-scale system of ocean currents that transport warm surface (1000 m) waters northward and return cooler waters southward is known as the Atlantic meridional overturning circulation (AMOC). Variations in the AMOC have significant repercussions for the climate system, hence there is a need for long term monitoring of AMOC fluctuations. Currently the longest record of continuous directly measured AMOC changes is from the RAPID-MOCHA-WBTS programme, initiated in 2004. The RAPID programme, and other mooring programmes, have revolutionised our understanding of large-scale circulation, however, by design they are constrained to measurements at a single latitude.

High global coverage of surface ocean data from satellite altimetry is available since the launch of TOPEX/Poseidon satellite in 1992 and has been shown to provide reliable estimates of surface ocean transports on interannual time scales. Here we show that a direct calculation of ocean circulation from satellite altimetry compares well with transport estimates from the 26° N RAPID array on low frequency (18-month) time scales for the upper mid-ocean transport (UMO; r = 0.75), the Gulf Stream transport through the Florida Straits (r = 0.70), and the AMOC (r = 0.83). The vertical structure of the circulation is also investigated, and it is found that the first baroclinic mode accounts for 83 % of the interior geostrophic variability, while remaining variability is explained by the barotropic mode. Finally, the UMO and the AMOC are estimated from historical altimetry data (1993 to 2018) using a dynamically based method that incorporates the vertical structure of the flow. The effective implementation of satellite-based method for monitoring the AMOC at 26° N lays down the starting point for monitoring large-scale circulation at all latitudes.

Alejandra Sanchez-Franks et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on os-2021-10', Anonymous Referee #1, 18 Mar 2021
  • RC2: 'Comment on os-2021-10', Anonymous Referee #2, 07 Apr 2021

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on os-2021-10', Anonymous Referee #1, 18 Mar 2021
  • RC2: 'Comment on os-2021-10', Anonymous Referee #2, 07 Apr 2021

Alejandra Sanchez-Franks et al.

Alejandra Sanchez-Franks et al.

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Short summary
In the North Atlantic, ocean currents carry warm surface waters northward and return cooler deep waters southward. This type of ocean circulation, known as overturning, is important for the Earth's climate. This overturning has been measured using a mooring array at 26° N in the North Atlantic since 2004. Here we use this mooring data and global satellite data to produce a new method for monitoring the overturning over longer timescales, which could potentially be applied to different latitudes.