Fig. 3

Vertical transect of seasonal mean geostrophic velocity (zonal velocity) along the Shiriya–Esan line calculated from shipboard observations (141.3°E obtained from JCOPE-T DA data) in a (e) winter, b (f) spring, c (g) summer, and d (h) autumn. Black contours denote the potential density anomaly, σ_θ. Eastward is positive. The dashed magenta line denotes the depth of the upper layer, H₁. Black bars in c, d, g, and h indicate the mean range of latitude for the upper- and lower-layer velocities, U₁ and U₂, respectively. The bathymetry is along 141.3°E. Gray contours in e–h denote eddy kinetic energy [m² s⁻²]