Abstract The Subei Shoal cold patch in the southwestern Yellow Sea exhibits an asymmetric life cycle, gradually intensifying from spring to summer followed by an unusually rapid decay in late summer—a feature not seen in other Yellow Sea cold patches. We use a high‐resolution, two‐way online nested model (1.2–1.5 km) to reproduce this life cycle and analyze the underlying dynamical mechanisms. It originates from tidal‐front upwelling along steep shelf topography, where secondary circulation transports bottom cold water to the surface. Its persistence is maintained by baroclinic forcing along temperature and salinity fronts, coupled with barotropic circulation driving surface divergence and bottom convergence, while nonlinear advection and viscous vorticity dissipation enhance vertical mixing. Cold patch intensity, quantified by the Topographic Position Index (TPI; lower values indicate stronger intensity), is modulated by wind stress, tidal cycles, and the Changjiang Diluted Water (CDW). Sensitivity experiments indicate that the CDW is critical: without it, local upwelling weakens by 43.3% and the patch decay is delayed fourfold. The rapid decline, occurring within ∼14 days, is triggered by abrupt changes in wind direction and seasonal shifts in CDW expansion, which disrupt the circulation supporting upwelling. These findings provide new insights into the mechanisms driving rapid transitions in coastal cold patches, with important implications for regional coastal upwelling dynamics.
Han et al. (Mon,) studied this question.