Fig. 1

Bathymetry and CTD stations in the northern South China Sea. Red dots are the CTD stations in summer. Topography is shown by the dotted, grey and black isobaths at 0m, 20m and 100m, respectively"

Fig. 2

Climatic temperature, thermal front (contour in 10-2℃∙km-1) and wind field (a), temperature, thermal front and wind field during in-situ observation period in 2017 (b). Contours in (a) and (b) denote the thermal front"

Fig. 3

Years of in-situ observation temperature, front intensity (black contour, unit: 10-2℃∙km-1), wind field (vector, unit: m·s-1) horizontal distribution"

Fig. 4

Vertical temperature (a, c) and thermal fronts (b, d) distribution of the sections D1 and D2 in June 2017. The white lines in (b) denote Richardson number, and the black contour is density"

Fig. 5

Maps of SST (shading) (a) and horizontal buoyancy gradient (shading) from the ROMS1 simulation. The grey line in (a) is the study section; the black vectors in (a) and (b) represent wind speed and velocity, respectively"

Fig. 6

Vertical profile of temperature, salinity (a) and buoyancy frequency (lg|N2|), density (b) from the ROMS; buoyancy frequency from in-situ observations (c). Contours in (a), (b) and (c) are salinity, density and density, respectively"

Fig. 7

Vertical slices of the log of the magnitude of horizontal buoyancy gradient (a), EPV (c) and its baroclinic component (b), the log of Richardson number (d). The yellow contours in (d) denote the critical value of 0.25 for Richardson number. The thick black lines represent density equal 22 kg∙m-3. The magenta contours in (c) show the critical value of zero for EPV"

Fig. 8

Snapshot of the EBF(a), curves of the sea surface EBF and EPV of study section (b). The location of the study section (b) is marked by the blue line in (a). The black (green) arrows denote wind speed (geostrophic currents)"