What Can We Learn From Observed Temperature and Salinity Isopycnal Anomalies at Eddy Generation Sites? Application in the Tropical Atlantic Ocean

• Published in: Journal of geophysical research. Oceans 2021-11, Vol.126 (11), p.n/a
• Main Authors: Aguedjou, H. M. A., Chaigneau, A., Dadou, I., Morel, Y., Pegliasco, C., Da‐Allada, C. Y., Baloïtcha, E.
• Format: Article
• Language: English
• Subjects: Advection; Altimetry; Anomalies; Anticyclones; Anticyclonic oceanic eddies; Atmospheric and Oceanic Physics; Bottom stress; Current rings; Cyclones; Diapycnal mixing; Drifters; Eddies; eddy generation mechanisms; Floats; Friction; Geophysics; isopycnal temperature/salinity anomalies; mesoscale eddies; Mesoscale phenomena; Mesoscale vortexes; Oceans; Physics; Potential vorticity; Salinity; Salinity effects; Satellite altimetry; Temperature anomalies; tropical Atlantic Ocean; Tropical climate; Vertical profiles; Vortices; Vorticity; Water masses; Wind stress
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2021JC017630

Based on 18 years of satellite altimetry data and temperature/salinity (θ/S) profiles from Argo floats, we analyze the isopycnal θ/S anomalies (θ'/S') within newborn eddies in the tropical Atlantic Ocean (TAO). Our results show that on density‐coordinates, both anticyclonic eddies (AEs) and cyclonic eddies (CEs) can exhibit positive, negative, or nonsignificant θ'/S'. Almost half of the sampled eddies do not have significant θ'/S' at their generation site. The other half exhibits significant positive or negative θ', up to ±0.5°C typically. More than 70% of them have a subsurface signature. Refined analyses of the vertical structure of new‐born eddies in three selected subregions show the dominance of cold (warm) subsurface AEs (CEs) likely due to isopycnal advection of large‐scale potential vorticity (PV) and θ. PV is a key parameter to analyze eddy generation and dynamics. Isopycnal advection, friction or diapycnal mixing can be involved in the generation of PV anomalies from which vortices can then emerge. However, it is difficult to evaluate PV at mesoscale. In this study, we propose to combine θ'/S' and PV anomalies to analyze which process could be involved in its transformation in the ocean. We argue that eddies created by diapycnal mixing or isopycnal advection of water‐masses are associated with PV anomalies and significant θ'/S'. In contrast, a frictional forcing also creates PV anomalies but without modifying θ/S. Even though our results remain qualitative, the proposed diagnostics can be of interest to validate realistic models and then use them to analyze the PV anomaly sources. Plain Language Summary Mesoscale vortices are common features in the global ocean, having typical length scales of 10–100 km and lifespans from several weeks to several months or even years for the more energetic structures. The vorticity of these quasicircular rotating structures emerging from large‐scale currents can be formed by several physical processes: isopycnal advection of a water mass, friction (wind stress, bottom stress), or diapycnal mixing. In this study, we first analyze the vertical structure of temperature/salinity in the eddies at their generation site. Based on the analysis of satellite and in situ data in the tropical Atlantic Ocean, we show that ∼50% of the eddies do not present significant isopycnal temperature anomalies when they are generated. In contrast, the remaining ∼50% of eddies present significant isopycnal temperature anomalies, but with