1078 / 2024-09-20 11:08:28

Dynamics paradigm of geostrophic cross-isobath transport (GCT) over highly variable shelf topographies

Geostrophic cross-isobath transport; along-isobath pressure gradient force; flow-topography interaction; topographically intensified upwelling

Flow-topography interaction is the key dynamics that governs the circulation over highly variable continental shelf, and its underlying dynamics remains as an active research topic. Based on results of observations and 3D process-oriented numerical modeling, we illustrated the 3D upwelling circulation and variability over the characteristic steep, concave, uniform (2D) and widened shelf topographic regimes in Northern South China Sea (NSCS). We presented the geostrophic cross-isobath transport (GCT) dynamics associated with the formation of the along-isobath pressure gradient force (PGF_y*) to interpret the unique circulation and variability of wind-driven upwelling circulation over these shelf topographic regimes. We found that an intensified upslope cross-isobath transport (u*) occurs locally over the steep, concave, and widened shelf regimes, as a result of GCT. Built on vorticity dynamics, we derived the GCT dynamics and analytically and numerically found that PGF_y*  over variable topographic regimes is induced by bottom stress curl arising from shear vorticity or curvature vorticity of the upwelling jet (v*) in a non-stratified flow with low Rossby number. Whereas nonlinearity and stratification predominate the GCT via nonlinear vorticity advection and the Joint Effect of Baroclinity and Relief (JEBAR). Meandering v* guided by variable shelf topography interacts with u* and jointly controls the variable upwelling circulation through flow-topography interaction. This study conducts holistic analyses based on the framework of GCT dynamics to enrich the wind-driven shelf circulation dynamics over different shelf topographic regimes.