Effects of Current Curvature on Topography‐Modulated Cross‐Isobath Motion in Northern South China Sea

Abstract Over continental shelves, shelf currents typically follow isobaths under the constraint of potential vorticity conservation. However, when the current curvature deviates from that of the underlying isobaths, it leads to intensified cross‐isobath motions, which play a critical role in facilitating exchange between coastal and open ocean waters. This study examines the topography‐modulated cross‐isobath motions over the Northern South China Sea (NSCS) shelf from the perspective of current curvature. Utilizing high‐resolution numerical simulations, we identify three regions, east of Hainan Island, south of Shanwei, and west of Taiwan Island, where convex topography disrupts the natural alignment between current curvature and isobaths. This misalignment leads to intensified downstream geostrophic cross‐isobath motion. Over those intensified cross‐isobath motion regions, shelf current curvature and cross‐isobath velocity exhibit consistent spatial and temporal patterns. Under the geostrophic balance in cross‐stream direction, the along‐stream dynamics of the shelf current are governed by the interplay of nonlinear advection, surface and bottom stress, and pressure gradient force (), with their cross‐stream variation shaped by topographic features. Analysis reveals that the current curvature, quantified by curvature vorticity, is primarily controlled by the nonlinear vorticity transport and the topography‐modulated current divergence/convergence (stretching effect) in summer. In winter, the generation of curvature vorticity is additionally influenced by the conversion of current shear through cross‐stream gradients in and bottom stress (banking effect), as well as bottom frictional stress term. These processes collectively shape the curvature structure of the shelf current and the associated cross‐isobath motion.