Seasonal variability and dynamics of coastal sea surface temperature fronts in the East China Sea

Fronts in coastal oceans are important mesoscale processes that relate to regional dynamics and can impact ecosystems. The daily distribution of a sea surface temperature (SST) front is obtained in the East China Sea (ECS) using 15 years of satellite observations. High frontal activities are mainly found near the coast. The spatial and temporal variability of the monthly frontal probability is subsequently investigated using an empirical orthogonal function (EOF). Seasonal variability in frontal activities is predominant for the majority of the ECS, with the highest and lowest values occurring during winter and summer, respectively. Some major fronts have been identified, such as coastal and shelf fronts. The coastal fronts can be further divided into three separate sections: near Hangzhou Bay and along the Jiangsu and Zhejiang coasts, respectively. The shelf fronts have two sections: north and south of the Changjiang River. All fronts are characterized by a prominent seasonal cycle, though their seasonalities differ. The underlying driving forces, e.g., alongshore wind, SST, and river discharge, are further analyzed for the individual fronts. River discharge is the driving factor of fronts to the south of the Hangzhou Bay along the Zhejiang coasts while wind is the main reason for the frontogenesis near and north of Hangzhou Bay. The SST largely influences the frontal dynamics for the shelf and coastal fronts to the north. This study comprehensively describes the frontal activities in the ECS and leads to a better understanding of frontogenesis in the coastal region. It is fundamentally helpful for fisheries management and has great potential for oceanic pollution control.