The Tilt of Mean Dynamic Topography and its Seasonality Along the Coast of the Chinese Mainland

Abstract

AbstractTilt of coastal mean dynamic topography (MDT) has recently been investigated in many regions, but few studies have examined the seasonality of the MDT along the coast of the Chinese mainland. The China seas are relatively unique as they experience prominent seasonal changes in monsoons and the China Coastal Currents, which are supposed to affect the coastal MDT significantly. This study investigates the Chinese coastal MDT tilt and its seasonality based on the geodetic and ocean approaches. The two independent approaches show a good agreement in their respective estimates. The Chinese coastal MDT presents an overall northward drop and undergoes an evident seasonality with steeper slopes in winter and flatter ones in summer. A dynamical analysis based on alongshore momentum equation suggests that the alongshore MDT along the coast of the Chinese mainland is a counter balance of contributions from the alongshore wind and the coastal current‐induced bottom friction, with both of them having prominent seasonality. The overall northward drop is in fact induced primarily by the strong alongshore wind stress in winter and by coastal currents in summer, in particular for the segment between Xiamen and Zhapo. The wintertime coastal MDT is well predicted by the arrested topographic wave model, which however could not reproduce the summertime tilt. The summertime MDT is more likely affected by the open‐ocean forcing (i.e., the latitudinal difference of the Kuroshio strength) and a return flow caused by flattening the coastal tilt piled up by the previous winter monsoon.