Unexpected abrupt cooling in bottom water driven by Typhoon Kong-Rey (2018) in the East China Sea

Typhoon interacts with the ocean by inducing vertical mixing, which alters the ocean’s internal temperature structure. Typically, after a typhoon passes, the surface water temperature decreases while the bottom water temperature increases due to this mixing. However, observations at 5, 20, 40 meter depths at the Ieodo Ocean Research Station (I-ORS) during Typhoon Kong-Rey (2018) revealed an unexpected abrupt cooling of the bottom water, different from the usual pattern. On October 6, 2018, at 00:00, Typhoon Kong-Rey (2018) passed ~86 km from I-ORS, causing the sharp decrease in bottom water temperature from 24.8℃ to 12.2℃, contrary to the typical warming observed in bottom waters. To explain this anomalous cooling, we analyzed temperature and current data from HYCOM. The HYCOM simulations indicated that the abrupt cooling of bottom water was driven by the southward movement of a subsurface cold water mass located north of I-ORS. The southward movement of the subsurface cold water mass can be partially attributed to Ekman currents and the southeastward tidal residual current. Our study provides a valuable example of short-term, anomalous bottom water temperature changes induced by a typhoon. It emphasizes the diverse oceanic responses to typhoons on the continental shelf of the East China Sea, underlining the complexity of typhoon-ocean interactions.