Observed Characteristics and Vertical Structure of Mesoscale Eddies in the Southwest Tropical Pacific

Abstract

In the Southwest Pacific Ocean, waters transit from the subtropical gyre before being redistributed equatorward and poleward. While the mean pathways are known, the contribution to the mixing and transport of the water from mesoscale eddies has not been comprehensively investigated. In this research, satellite altimetry data, combined with an eddy detection and tracking algorithm is used to investigate the distribution and surface characteristics of mesoscale eddies in this region of complex bathymetry (10°S–30°S, 140°E–190°E). Detected eddies are then colocalized with in situ data from Argo floats to determine their vertical structure and the effect of eddies on the water masses. The numerous islands affect the eddy behavior as most eddies are formed in the lee of islands, propagate westward and decay when encountering shallow bathymetry. Eddies are sparse and short‐lived in the tropical area north of Fiji, impacting only the top 200 meters of water. They do not appear to be able to trap and transport waters in this region. In the Coral Sea, a region of lateral shear between currents transporting waters of different origins, eddies are more numerous and energetic. They affect the water properties down to at least 500 m depth, and anticyclonic eddies trap water to ∼200 m, contributing to the upper thermocline waters mixing and transport. South of New Caledonia, mesoscale eddies are ubiquitous, with typical lifetimes longer than 5 months. They affect the temperature, salinity, and velocities down to ∼1,000 m depth, and weakly contribute to the mixing of lower thermocline waters.

Oceanic vortex mergers are not isolated but influenced by the β-effect and surrounding eddies

“…This increases the merging efficiency as well as d m i . The merging distances observed in the HYCOM dataset are reproduced by the idealized simulations on the f-plane: the values of d m i match well the observed d m for all Ro and Bu studied (in particular for simulations with H = 1000 m and α = 2, as expected -in the ocean, eddies are mostly Gaussian 37 , and about 1000 m deep [41][42][43][44] ). With the β-effect, if eddies are not constrained by a disk, d m in the HYCOM dataset is significantly larger than the d m i values observed in idealized simulations, especially for small Bu and Ro.…”

Aspect Ratio of Eddies Inferred From Argo Floats and Satellite Altimeter Data in the Ocean

“…Our results show that the penetrating depth D of eddies in this region is approximately 800 m, which agrees well with the previous authors' conclusions. Based on the salinity and temperature anomalies in the Southwest Pacific Ocean (10°S–30°S, 140°E–190°E), Keppler et al () showed that on average, eddies in these locations are more deep‐reaching than those found toward the north of the study region. Their findings show that the penetrating depth of eddies is between 400 and 1,000 m, and our results are consistent with their findings (Table and Figure a).…”

“…In the present study, to investigate the aspect of an eddy, only the T/S profile at the eddy center is needed to calculate the buoyancy frequency N c (see formula (10)). Following Keppler et al () and Sun et al (), all profiles in which a float is trapped inside the eddies (as determined by the altimeter observations) satisfy the following conditions: Argos' position coordinates were transformed into an eddy‐centered polar coordinate system normalized by the eddy radius. Therefore, an Argo float accurately situated at the eddy center will have the coordinates ( Δr = 0), for an Argo float accurately situating at the boundary of an eddy will have coordinates ( Δr = 1).…”

Closing the Gap Between the Coral Sea and the Equator: Direct Observations of the North Australian Western Boundary Currents

“…How valid are the seasonal cycles from the gliders in the presence of both eddies and interannual variations, with the irregular and limited temporal distribution of the glider deployments? In terms of eddies, Keppler et al () found that mesoscale eddies west of Vanuatu are numerous and energetic and affect the water properties down to at least 500 m. However, their results also show that along the Queensland boundary, the eddy numbers, radius, amplitude, and EKE are much reduced—their influence on the boundary currents may in fact be quite low. Results from OFAM3.0 using the glider temporal sampling (on the tracks in Figure ) produce seasonal patterns at least qualitatively similar to climatological values (Figure S6).…”