Fig. 1

Averaged horizontal distribution of sea surface height anomalies (a, b, c) and surface geostrophic eddy kinetic energy (d, e, f) from May to October, 1994 to 2015. The averaged spatial distribution of sea surface height anomalies (a, b, c), obtained from CMEMS, HYCOM, and spatially filtered HYCOM data, respectively. The black arrows represent geostrophic current anomalies, while the shading represents the sea surface height anomalies. The averaged spatial distribution of surface geostrophic eddy kinetic energy (d, e, f) is also presented, generated from CMEMS, HYCOM, and spatially filtered HYCOM data, respectively. The shading represents surface geostrophic eddy kinetic energy"

Fig. 2

Eddy extraction flow diagram"

Fig. 3

Schematic diagram of energy conversion. Only the energy conversion terms related to EKE and EPE are shown"

Fig. 4

Time series of the SLD’s area (a), amplitude (b), vorticity (c), as well as its trajectory (d). The blue and red lines in d are the trajectories of the SLD identified by HYCOM and CMEMS, respectively. The blue and red dates are the generation and extinction times of the SLD. The CMEMS-found SLD first forms on May 18 and decays on September 6, and the HYCOM-found SLD first forms on May 23 and decays on September 5"

Fig. 5

Time series of the mean wind stress curl over SLD calculated from NCEP CFSR and CFSv2 (blue line), CCMPv2 (red line) wind field data, respectively"

Fig. 6

The time series of volume-integrated (0~200 m) EKE in the SLD region. FDVS, MS, WS, SS, SDVS and DCS represent the first development stage, mature stage, weakening stage, stable stage, second development stage and decay stage of SLD, respectively. The black dashed line indicates the standard deviation of EKE, and the red dotted line indicates the dividing line between the stages"

Fig. 7

The vertical profiles of density anomaly along the longitude (a1~f1) and latitude (a2~f2) of the SLD’s center during the first development stage (a1~a2), mature stage (b1~b2), weakening stage (c1~c2), stable stage (d1~d2), second development stage (e1~e2) and decay stage (f1~f2) of the SLD. The mean values for the corresponding stages are shown, where the shading indicates density anomaly. The black contours indicate the zonal current anomaly (a1~f1) and meridional current anomaly (a2~f2) respectively, with a spacing of 0.1 m·s-1, the solid lines represent positive values, while the dashed lines represent negative values. The SLD region is shaded in gray"

Fig. 8

Spatial distribution of temperature (unit: ℃) and salinity (unit: ‰) in the first development stage (a1~a3), mature stage (b1~b3), weakening stage (c1~c3), stable stage (d1~d3), second development stage (e1~e3) and decay stage (f1~f3) of the SLD at depths of 10 m (a1~f1), 150 m (a2~f2) and 350 m (a3~f3), respectively. The mean values of the corresponding stages are shown in the figure, where the shading indicates temperature, the green closed contour indicates SLD, the red dots indicate the SLD centers, and the black contour is salinity. The thickened black contour at 10 m depth indicates a 34.4‰ salinity contour, and at 150 m depth, a 34.92‰ salinity contour"

Fig. 9

Spatial distribution of depth-integrated (0~200 m) EKE (a, b) and EPE (c, d) on May 23 (a, c) and June 10 (b, d). Green closed contours indicate SLD; black arrows indicate the geostrophic current, and only the part of the velocity greater than 0.2 m·s-1 is plotted in order to fully represent the major axis of SMC"

Fig. 10

Spatial distribution of depth-integrated (0~200 m) eddy energy: eddy kinetic energy (a1~f1) and eddy available potential energy (a2~f2), energy conversion rate: the wind stress work (a3~f3), the barotropic MKE→EKE conversion (a4~f4), the baroclinic MPE→EPE conversion (a5~f5), the baroclinic EPE→EKE conversion (a6~f6), the EKE advection (a7~f7), the EPE advection (a8~f8) and the pressure work (a9~f9) during the first development stage (a1~a9), mature stage (b1~b9), weakening stage (c1~c9), stable stage (d1~d9), second development stage (e1~e9) and decay stage (f1~f9) of the SLD, with green closed contours indicating SLD and black arrows for the geostrophic current"

Fig. 11

Vertical distribution of eddy energy: eddy kinetic energy (a1~a2) and eddy available potential energy (b1~b2), and energy conversion rate: the barotropic MKE→EKE conversion (c1~c2), the baroclinic MPE→EPE conversion (d1~d2), the baroclinic EPE→EKE conversion (e1~e2), the EKE advection (f1~f2), the EPE advection (g1~g2) and the pressure work (h1~h2) along the longitude (a1~f1) and latitude (a2~f2) of the SLD’s center at the mature stage of the SLD. The gray shaded area is the SLD region, and the thickened black contours indicate 5 J·m-3 and ±1 10-5 W·m-3, respectively, the solid lines represent positive values, while the dashed lines represent negative values"

Fig. 12

Spatial distribution of depth-integrated (0~200 m) EKE (a, b) and EPE (c, d) on August 26 (a, c) and September 5 (b, d). The closed green contours represent the SLD. The black arrows denote the geostrophic current. Only the part of the velocity greater than 0.2 m·s-1 is plotted in order to effectively depict the major axis of SMC"

Fig. 13

The comparison of volume-integrated (0~200 m) eddy energy (a) and energy conversion terms (b) in the SLD during the first development stage (FDVS), mature stage (MS), weakening stage (WS), stable stage (SS), second development stage (SDVS), and decay stage (DCS). EKE represents the eddy kinetic energy, EPE represents the eddy available potential energy, ${{\text{F}}_{\text{k}}}$ represents the wind stress work, BTC represents the barotropic MKE→EKE conversion, BCC represents the baroclinic MPE→EPE conversion, VEDF represents the baroclinic EPE→EKE conversion through vertical eddy density flux, $\text{AD}{{\text{V}}_{\text{k}}}$ represents the EKE advection, ADVp represents the EPE advection, and PW represents the pressure work"