Figure  1.  Typhoon MITAG tracks, glider paths (cyan dots), and the locations of Argo floats (magenta dots). The black shadow indicates the Kuroshio.

Figure  2.  Corrected errors (Profile 19) including thermal lag correction and burring of salinity.

Figure  3.  The time series vertical distribution of potential temperature (a), salinity (b), potential density (c), and calculated buoyancy frequency (d). The latitudes at which the gilder was located on certain days were also marked on the top. The white solid lines denote the MLD, the magenta dashed line indicate that the change in direction of glider, the white and black dashed lines indicate the period of passing east of Luzon Strait for typhoon MITAG (Fig. 1), and the blue dashed lines in b suggest the boundaries of the high salinity water mass (>34.8).

Figure  4.  The time series vertical distribution of potential temperature anomaly (a), salinity anomaly (b), potential density anomaly (c), and mean vertical temperature (d). The latitudes at which the gilder was located on certain days were also marked on the top. The white solid lines denote the MLD, the magenta dashed line indicate that the change in direction of glider, the white and black dashed lines indicate the period of passing east of Luzon Strait for typhoon MITAG (Fig. 1), and the blue dashed lines in b suggest the boundaries of the high salinity water mass (>34.8).

Figure  5.  T-S diagrams of CS1/2 and Argo profiles (a) and the climatology salinity maximum at a depth of 0–400 m for September (b) and October (c), respectively. In a, the blue thick line represents the averaged T-S curves for the northeastern SCS water (SCSW), the red thick line represents Kuroshio water (KW), based on WOA 18 climatology data, and the black contours represent potential density (σ_θ). The rectangles in b indicate the sampling location of different water masses: the northeastern SCS Water (SCSW, 18°–22°N, 116°–120.5°E) is marked in blue, and the Kuroshio water (KW, 18°–22°N, 122°–124°E) is indicated in red. The cyan dots in c are glider paths, and the magenta dots are locations of Argo floats.

Figure  6.  Potential temperature (a), salinity (b), and potential density (c) by Argo float, respectively, and calculated buoyancy frequency (d). The white solid lines denote the MLD, the white and black dashed lines indicate the period of passing east of Luzon Strait for typhoon MITAG (Fig. 1).

Figure  7.  Time evolution of the SLA (m) and geostrophic currents (m/s) from September 28 to October 14, 2019. Regions shallower than 200 m are masked. The observed section is represented by cyan dots. The positions of the glider during that day are denoted by red dots. The yellow and magenta dots are the trajectories of typhoon and Argo float, respectively. The green rectangular frame is used to show the axis of the Kuroshio current, and the blue boxes is area in which the variations of total relative vorticity and EPV are calculated. The cyclonic and anti-cyclonic eddies in the blue box are denoted as “CE” and “AE”.

Figure  8.  Variations of the Kuroshio current during the study period, represented by the geostrophic current meridional velocity (m/s). a. The movement of the Kuroshio current axis from 120.125°E to 121.875°E. The contour map indicates the northward meridional vector of the Kuroshio current. Each grid represents a velocity maximum and their longitude in the green rectangular (20.125°–21.875°N, 120.125°–121.875°E) in Fig. 7a. The black dots are the position of the Kuroshio current main axis. b. The velocity variation of the Kuroshio current main axis near 21°N. c. The velocity variation of the Kuroshio current main axis near 18.5°N. d. The variation of total relative vorticity in the CE (blue line) and AE (red line) and EPV (orange and green lines) in the blue box (18°–22°N, 122°–124°E) in Fig. 7. The orange line indicate the total EPV calculated in the box of (18°–22°N, 122°–124°E), and green line indicate the total EPV calculated in the box of (18°–20°N, 122°–124°E). The positive value of EPV indicate the Ekman upwelling. e. The variation of SLA in the center of CE (blue line) and AE (orange line).

Figure  9.  Distribution of wind field, wind stress curl (a, b, c) and Ekman transport (d, e, f) when the typhoon passed east of the Luzon Strait. The contour maps in a, b, and c display the wind curl, and the arrows indicate the wind velocity and direction. The contour maps in d, e, and f show the Ekman transport per unit width, and the arrows represent directions.