Observed 3D Structure, Generation, and Dissipation of Oceanic Mesoscale Eddies in the South China Sea

Abstract

Oceanic mesoscale eddies with horizontal scales of 50–300 km are the most energetic form of flows in the ocean. They are the oceanic analogues of atmospheric storms and are effective transporters of heat, nutrients, dissolved carbon, and other biochemical materials in the ocean. Although oceanic eddies have been ubiquitously observed in the world oceans since 1960s, our understanding of their three-dimensional (3D) structure, generation, and dissipation remains fragmentary due to lack of systematic full water-depth measurements. To bridge this knowledge gap, we designed and conducted a multi-months field campaign, called the South China Sea Mesoscale Eddy Experiment (S-MEE), in the northern South China Sea in 2013/2014. The S-MEE for the first time captured full-depth 3D structures of an anticyclonic and cyclonic eddy pair, which are characterized by a distinct vertical tilt of their axes. By observing the eddy evolution at an upstream versus downstream location and conducting an eddy energy budget analysis, the authors further proposed that generation of submesoscale motions most likely constitutes the dominant dissipation mechanism for the observed eddies.

Ocean Circulation in the Western Gulf of Mexico Using Self‐Organizing Maps

“…The pattern was not visible at 200‐m depth in the presence of cyclones formed by the current stream (offshore direction) of the northern portion of the LCE. Group 1 also revealed a downscale energy transfer as a result of the LCE collision producing subsurface cyclones and jets as a dissipation mechanism, which has also been reported by Hyunn and Hogan () in the GoM and by Zhang et al () in the South China Sea.…”

Submesoscale Features and Turbulent Mixing of an Oblique Anticyclonic Eddy in the Gulf of Alaska Investigated by Marine Seismic Survey Data

“…Even though a historical seismic survey has no specific purpose of eddy detection, it is often easy to capture the ubiquitous eddies with coherent structures especially in the middle‐ to high‐latitude oceans. The notion of structurally symmetric eddies has been widely accepted; however, tilted eddies in the oceans are possible as well (Canals et al, ; Zhang et al, ). Our fine‐scale observation confirms the existence of a strongly tilted eddy and allows us to look into the detailed submesoscale processes.…”

Vertical structure anomalies of oceanic eddies in the Kuroshio Extension region

“…For example, the horizontal temperature gradient of the eddy increase with depth from the surface to 100 m and then decreases with depth below 100 m; the cold core was evident from the surface to 300 m depth, with 1–2°C cooler temperature than its surrounding; the tangential velocity of the eddy, reaching 30–40 cm/s above 50 m, decreased with depth, and was less than 5 cm/s at 300 m depth. There were also other case studies based on in situ measurements data [e.g., Martin et al ., ; Dong et al , ; Hu et al ., ; Zhang et al ., ; Zhang et al ., ]. Although these case studies revealed some information about oceanic eddies, they were too limited in measured data to uncover eddy's 3‐D structure.…”

“…About 90% eddies are bowl‐shaped. Field experiments have observed two types of data: bowl‐shaped and lens‐shaped [e.g., Hu et al ., ; Zhang et al ., ]. The modeling results and observational data agree with each other quite well, though the cone‐shaped eddies are not reported in observation, which could be caused by either the difficulty in measurements of 3‐D eddies or the existence of the small number of the cone‐shaped eddies.…”