Bypassing Typhoons Cause Three-dimensional Dramatic Changes in Temperature and Ocean Heat Content of the Yellow Sea and Bohai Sea: A Case Study with Super Typhoon Maysak (2020)

The Yellow Sea and Bohai Sea are among the global shelf seas susceptible to typhoons every year. Using observations and high-resolution numerical simulations, the current study investigates the dramatic changes in temperature and ocean heat content (OHC) of the Yellow Sea and Bohai Sea caused by Super Typhoon Maysak in early September 2020, which is representative of northward/northeastward-bypassing typhoons with centers just to the east of the study area. Temperature shows spatially coherent cooling in the upper mixed layer but warming in the subsurface layer in the majority of the offshore waters, due to wind-enhanced vertical mixing. In lower layers from the thermocline to sea bottom, temperature experiences significant warming in northeastern coastal waters of the Shandong Peninsula and in regions just off the Subei Shoal, but significant cooling in western coastal waters of the Korean Peninsula and southern coastal waters of the Shandong Peninsula. Significant temperature warming/cooling in lower layers is caused by coastal downwelling/upwelling. The total OHC of the study area decreases rapidly during Typhoon Maysak (2020)’s passage, which is generated comparably by latent heat loss at the sea surface and southward heat advection out of the study area at the southern boundary. Reduced shortwave radiation contributes positively but secondarily to the decreasing OHC during the first day. A numerical experiment suggests that Typhoon Maysak (2020)-induced OHC decline could have greatly affected the regional climate evolution in the following seasons. More studies are needed to fully understand the impacts of typhoons on regional climate changes in shelf seas at different time scales.