Up to now, submesoscale motions are hot spots in ocean research, which have significant effects on material exchange and energy cascade. However, submesoscale motions in coastal regions are rarely studied which are affected by multiple factors such as river, tide, topography, wind and so on. Here, we use a high-resolution ROMS model to simulate submesoscale currents in the Zhe-min coastal area. Submesoscale motions are active associated with high values of buoyancy gradient, divergence, straining, vertical velocity, and submesoscale kinetic energy. In seasonal variation, submesoscale motions are more active in winter than in summer, with positive skewness of relative vorticity due to centrifugal instability, when the Zhe-min coastal front appears and enhances. Monsoon is a crucial factor in generating submesoscale motions. When down-front winds blow strongly, Ekman transport extracts PV from surface and bottom boundary layer, and then triggers symmetric instability (SI). After the weakening of down-front winds, SI disappears, followed by mixed mode and baroclinic instability (BI). This mechanism is different from that in deep ocean because of shallow topography where the whole water column can be mixed. In restratification, TTW is an important process against Ekman transport forced by winds. Besides, Frontogenesis is also crucial for submesoscale generation and restratification. These submesoscale processes that are strengthened in winter and modulated by wind play vital roles in material exchange in the Zhe-min coastal area.

instability, submesoscale processes, front, coastal regions