Three-dimensional thermohaline anomaly structures of rings in the Kuroshio Extension region
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Abstract: Using AVISO satellite altimeter observations during 1993–2015 and a manual eddy detection method, a total of 276 anticyclonic rings and 242 cyclonic rings shed from the Kuroshio Extension (KE) were identified, and their three-dimensional (3D) anomaly structures were further reconstructd based on the Argo float data and the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) cruise and buoy data through an interpolation method. It is found that the cyclonic (anticyclonic) rings presented consistent negative (positive) anomalies of potential temperature; meanwhile the relevant maximum anomaly center became increasingly shallow for the cyclonic rings whereas it went deeper for the anticyclonic rings as the potential temperature anomaly decreased from the west to the east. The above deepening or shoaling trend is associated with the zonal change of the depth of the main thermocline. Moreover, the composite cold ring between 140° and 150°E was found to exhibit a double-core vertical structure due to the existence of mode water with low potential vorticity. Specifically, a relatively large negative (positive) salinity anomaly and a small positive (negative) one appeared for the composite cyclonic (anticyclonic) ring at the depth above and below 600 m, respectively. The underlying driving force for the temperature and salinity anomaly of the composite rings was also attempted, which varies depending on the intensity of the background current and the temperature and salinity fields in different areas of the KE region, and the rings’ influences on the temperature and salinity could reach deeper than 1 000 m on average.
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Figure 1. An example of a cyclonic ring shed from the Kuroshio Extension (KE) jet at (31.0°N, 154.5°E). a–f. The temporal evolution of this cyclonic ring from 16 September 2005 to 23 January 2006, respectively. Color indicates absolute dynamic topography (cm), and black contour the path of the KE axis and the pinched-off ring.
Figure 2. Floats distribution and main water masses in the study regions. a. The spatial distribution of floats available in the KE region, with the number of floats shown in 1°×1° bin in the period 1999–2015; b. The mean potential temperature-salinity diagrams; and c. the mean potential vorticity (PV) diagrams for sub-regions B to E, calculated with all float profiles outside the eddies. NPTW: North Pacific Tropical Water; L-CMW: Lighter Center Mode Water; NPIW: North Pacific Intermediate Water; and STMW: Subtropical Mode Water.
Figure 3. The mean vertical profiles of potential temperature anomaly
$\theta '$ (°C) for the anticyclonic and cyclonic rings in the three sub-regions. The blue and red curves in each diagram represent the anomaly for the cyclonic and anticyclonic rings, respectively. The shading indicates one standard deviation.
Figure 4. Vertical sections of potential temperature anomaly (θ´) of composite cyclonic (top) and anticyclonic (bottom) rings at
${\rm{\Delta }}y = 0$ in sub-regions B, C, and D.
Figure 5. Mean vertical profiles of potential temperature based on the profiles outside eddies. The frame in red indicates the depth of the main thermocline.
Figure 6. Horizontal distributions of potential temperature anomaly (
$\theta '$ ) of the composite cyclonic rings (the left three columns) and anticyclonic rings (the right three columns) at depths of 10, 150, 300, 450, 600, 900, and 1 200 m in sub-regions B, C, and D, respectively.
Figure 7. Mean vertical profiles of salinity anomaly (S') for anticyclonic and cyclonic rings in all sub-regions. The blue and red curves represent the anomaly for the cyclonic and anticyclonic rings, respectively. Shading indicates one standard deviation.
Figure 8. Vertical sections of salinity anomaly (S′) of the composite cyclonic rings (top) and the anticyclonic rings (bottom) at
${\rm{\Delta }}y = 0$ in sub-regions B, C, and D.
Figure 9. Horizontal distributions of salinity anomaly (
$S '$ ) of composited cyclonic rings (the three left columns) and anticyclonic rings (the three right columns) at depths of 10, 150, 300, 450, 600, 900, and 1 200 m in sub-regions B, C, and D.Table 1. Statistics of the rings shed from the KE jet from 1993 to 2015
Number Amplitude/cm Lifetime/d radius/km all reabsorbed Region B 160 87 34.9/37.6 52/60 96.7/82.5 Region C 169 113 33.9/37.3 43/69 103.9/92.4 Region D 139 87 28.5/34.0 42/43 109.1/102.4 Region E 49 35 25.3/29.7 46/37 116.0/109.5 Note: The data separated by a slash are those of the anticyclonic/cyclonic rings. 
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Table 2. The floats caught by rings and inside the range of twofold radius of rings in each sub-region
Number Floats caught by rings Inside the range of twofold radius of rings Outside rings Region B 30 182 173/140 704/799 13 714 Region C 19 615 156/206 950/759 10 058 Region D 13 318 61/104 509/297 6 457 Region E 8 299 17/25 77/108 4 598 Note: The values separated by a slash are those of the anticyclonic rings/cyclonic rings.
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