In three consecutive years from 2016 to 2018, extreme ocean warming events, or marine heatwaves (MHW), occurred during boreal summers in the East China Sea (ECS) and South Yellow Sea (SYS), which was unprecedented in the past four decades based on the satellite record. In this study, we used a high-resolution hydrodynamic model based on FVCOM (Finite Volume Community Ocean Model) to simulate the evolution of these warming events. An upper ocean temperature budget (0-20m) analysis based on the model results shows that the shortwave radiation and the ocean advection anomalies jointly contributed to the anomalous warming in the three successive summers (June-August) in the SYS and the north part of the ECS. In addition, the reduction of surface wind speeds during the 2016 and 2017 summers further weakened the vertical mixing, thereby enhancing the anomalous warming in the north part of the ECS adjacent to the SYS. During the three summers, the increases of shortwave radiation were closely related to the East Asian Summer Monsoon variability, which reduced the cloud cover in the ECS and SYS, whereas the advection anomalies were mostly associated with regional wind anomalies. In summer 2018, upper ocean heat was transported into the central trough of the South Yellow Sea, accumulated in an anticyclonic eddy generated by the anomalous wind stress curls. Understanding the drivers of the MHWs can help MHW predictions in the coastal region, in order to help the fisheries and aquaculture industries to better manage the environmental risks under a warming climate.

The impact of high-frequency atmospheric forcing on the Yellow Sea (YS) circulation with emphasis on the Yellow Sea Warm Current (YSWC) was investigated by comparing model simulations with and without high-frequency atmospheric processes. By including the high-frequency atmospheric forcing at the synoptic scale in an atmosphere reanalysis used to force the ocean model, the simulated intensity of the mean YSWC is increased by 40-100%. The mean temperature is decreased by up to 1°C, and the mean salinity along the YSWC pathway is increased by up to 0.2-0.5 psu. Additional simulations in which either the wind or other atmospheric fields were filtered revealed that the high-frequency wind forcing is more important in the YSWC and relates mean temperature with the other atmospheric variables that play relatively minor roles. In winter, the high-frequency wind forcing associated with frequent winter storm bursts and relaxation is able to excite coastal trapped waves propagating cyclonically around the Bohai Sea and Yellow Sea coast; this forcing is a very important factor influencing the synoptic variability in the YSWC and drives intermittent warm and salty water intrusion into the southern YS. The results from this study provide a basis for a new understanding of how transient atmospheric phenomena, such as winter storms, impact regional circulation and water transport in the YS.

In three consecutive years from 2016 to 2018, extreme ocean warming events, or marine heatwaves (MHW), occurred during boreal summers in the East China Sea (ECS) and South Yellow Sea (SYS), which is unprecedented in the past four decades based on the satellite record. In this study, we used a high-resolution hydrodynamic model based on FVCOM (Finite Volume Community Ocean Model) to simulate the evolution of these warming events. An upper ocean temperature budget (0-20m) analysis based on the model results shows that the shortwave radiation and the ocean advection anomalies jointly contributed to the anomalous warming in the three successive summers (June-August) in the SYS and the north part of the ECS. In addition, the reduction of surface wind speeds during the 2016 and 2017 summers further weakened the vertical mixing, thereby enhancing the anomalous warming in the north part of the ECS adjacent to the SYS. During the three summers, the increases of shortwave radiation were closely related to the East Asian Summer Monsoon (EASM) variability, which reduced the cloud cover in the ECS and SYS, whereas the advection anomalies were mostly associated with regional wind anomalies. In summer 2018, upper ocean heat was transported into the central trough of the South Yellow Sea, accumulated in an anticyclonic eddy generated by the anomalous wind stress curls. Therefore, despite the primary driver of the MHWs is the EASM variation, regional processes are critical to driving the spatial pattern of the MHW intensity in the ECS and SYS.