Decadal Variation in Winter‐Spring Thermal Front to the Zhejiang‐Fujian Coast and Its Mechanism

Abstract Off the east shore of China, thermal front plays a crucial role in modulating coastal biogeochemical environment. Based on multi‐source observational and reanalysis products, decadal variation and regulatory mechanism of Zhejiang‐Fujian coastal front (ZFCF) were investigated. The intensity of ZFCF showed a two‐stage inversed varying trend over past four decades: a downtrend from 1982 to 2002 followed by an uptrend from 2002 to 2022. During 1982–2002, sea surface temperature (SST) experienced more pronounced warming in inshore areas than offshore due to weakening of the southward coastal current, and this primarily led to the downtrend of ZFCF. Within 2002–2022, opposite SST trends were observed on two sides of ZFCF, that is, the ZFCF kept intensifying due to the cooperation of cooling inshore and warming offshore. The enhanced coastal current driven by stronger monsoon and increased Yangtze River discharge cooled the inshore area, then the cooling was further facilitated by intensified heat loss in the upper layer of the plume. Meanwhile, the onshore shift of Kuroshio led to strengthened intrusion of warm water into the East China Sea, heating the offshore side of ZFCF and thus intensifying the front.