Abnormal Sea Surface Warming and Cooling in the East China Sea during Summer

Abstract

To understand changes in sea surface temperature (SST) in the East China Sea (ECS) during summer, we analyzed relationships among SST, air temperature (AT), and heat flux using satellite, model, and in situ data from 2003 to 2019. SST variation was correlated with AT variation (R-2 = 0.65). Spatial variation in SST was higher in the northern ECS, and this pattern was controlled by atmospheric forcing. In the southern ECS, changes in SST were less pronounced and were influenced by the branch of the Kuroshio Current (BKC). To analyze abnormal SST warming and cooling events, SST anomalies were used to classify positive and negative periods and to determine years with abnormal changes in SST. Abnormal warming periods were identified in August of 2016 and 2017, and abnormal cooling periods were identified in August of 2011 and 2014. SST was significantly greater in August 2016 relative to the remainder of the study period. An influx of low-salinity water likely contributed to this warming, which was then enhanced by stratification that blocked exchange between the surface and deep water. In August 2017, sea surface warming was likely related to increasing in the BKC. In August 2011, SST was lower than AT due to increased mixing between surface and deep water caused by typhoons. Finally, in the August 2014, SST was higher than AT, likely related to weakening in the East Asian Summer Monsoon (EASM).