Anatomy of a Cyclonic Eddy in the Kuroshio Extension Based on High-Resolution Observations

Abstract

Mesoscale eddies are common in the ocean and their surface characteristics have been well revealed based on altimetric observations. Comparatively, the knowledge of the three-dimensional (3D) structure of mesoscale eddies is scarce, especially in the open ocean. In the present study, high-resolution field observations of a cyclonic eddy in the Kuroshio Extension have been carried out and the anatomy of the observed eddy is conducted. The temperature anomaly exhibits a vertical monopole cone structure with a maximum of −7.3 • C located in the main thermocline. The salinity anomaly shows a vertical dipole structure with a fresh anomaly in the main thermocline and a saline anomaly in the North Pacific Intermediate Water (NPIW). The cyclonic flow displays an equivalent barotropic structure. The mixed layer is deep in the center of the eddy and thin in the periphery. The seasonal thermocline is intensified and the permanent thermocline is upward domed by 350 m. The subtropical mode water (STMW) straddled between the seasonal and permanent thermoclines weakens and dissipates in the eddy center. The salinity of NPIW distributed along the isopycnals shows no significant difference inside and outside the eddy. The geostrophic relation is approximately set up in the eddy. The nonlinearity-defined as the ratio between the rotational speed to the translational speed-is 12.5 and decreases with depth. The eddy-wind interaction is examined by high resolution satellite observations. The results show that the cold eddy induces wind stress aloft with positive divergence and negative curl. The wind induced upwelling process is responsible for the formation of the horizontal monopole pattern of salinity, while the horizontal transport results in the horizontal dipole structure of temperature in the mixed layer. species composition (EDDIES) in the Sargasso Sea off Bermuda [5], meso-and submesoscale processes in an intense front (AlborEx) [6] and the northwestern Pacific eddies, internal waves and mixing Experiment (NPEIM) [7], and so forth. Nowadays, main observation methods for field experiment include Argo floats, moored instrumentation, underwater gliders and shipboard survey.Argo profiling floats, which are designed to measure underwater ocean temperature and salinity (T/S) [8], are one of the effective methods to obtain 3D mesoscale eddy structures [9][10][11][12][13]. However, due to the drift features, the detailed structure of a specific eddy is difficult to acquire unless a large number of Argo floats are deployed inside the targeted mesoscale eddy. Reference [14] deployed 17 rapid-sampling Argo floats to study the anticyclonic eddies effects on mode water subduction in the south of the Kuroshio Extension to the east of Japan. In situ mooring observations can usually collect temperature, salinity and current data from the bottom to the surface at a fixed-point where the eddy moves through. Reference [15] designed and conducted a multi-month field campaign to capture the full-depth 3D structure of a pair of anticyclonic and c...

Parametric Model for Eddies‐Induced Sound Speed Anomaly in Five Active Mesoscale Eddy Regions

“…A cyclonic eddy field observation experiment was conducted over the area (156°E–160°E, 30.33°N–32°N) from June 26 to 30, 2014, with a total cruising distance of approximately 1,674 km (Figure 2) (Zhang et al., 2019). Zhang et al.…”

“…Zhang et al. (2019) established a field experiment with six zonal routes from south to north. The route closest to the eddy center (marked with a magenta square) is named S3.…”

“…The cyan line is the −0.1 m contour of surface level anomalies, which indicates the boundary of the cyclonic eddie (CE) in Zhang et al. (2019), and the black line is the 0.4 m/s contour of geostrophic velocity. The magenta square is the geometric center of the CE defined in the META 2.0 product (https://www.aviso.altimetry.fr/en/data/products/value-added-products/global-mesoscale-eddy-trajectory-product.html), which is closest to the survey line marked as S3.…”

“…The data collected in the layer of 5-1,000 m are used here. We refer the reader to Zhang et al (2019) for further information about this experiment.…”

“…A cyclonic eddy field observation experiment was conducted over the area (156°E-160°E, 30.33°N-32°N) from June 26 to 30, 2014, with a total cruising distance of approximately 1,674 km (Figure 2) (Zhang et al, 2019). Zhang et al (2019) established a field experiment with six zonal routes from south to north. The route closest to the eddy 2019), and the black line is the 0.4 m/s contour of geostrophic velocity.…”