Three‐Dimensional Temperature Responses to Northward‐Moving Typhoons in the Shallow Stratified Yellow Sea in Summer

Abstract

AbstractCharacterized by a sharp thermocline and large cold‐water mass below, the Yellow Sea (YS) in summer is a shelf sea that is one of the most vulnerable to typhoons in the world. With observations and high‐resolution numerical simulations, we investigated the three‐dimensional temperature changes and underlying dynamics during the passage of Typhoon Bavi in August 2020, which was representative of northward‐moving typhoons in the eastern YS. Bavi's cyclonic strong winds caused intense turbulent mixing and Ekman divergence. The intense vertical mixing generated spatially coherent temperature cooling in the surface layer and partly caused temperature warming in the subsurface layer on both sides of the typhoon track. The largest surface cooling and subsurface warming both occurred on the right side of the typhoon track. Wind‐induced Ekman divergence generated two overturning circulation systems zonally across the YS, consisting of upper layer shoreward currents, coastal downwelling, lower layer seaward currents and upwelling on the typhoon track. Downwelling and seaward currents caused temperature warming below the thermocline, especially in the bottom layer. Upwelling shoaled the thermocline, resulting in subsurface cooling on the typhoon track. Additionally, Ekman divergence produced sea surface height minima on the typhoon track, causing strong southward barotropic currents to the left, which subsequently drove strong temperature cooling above the southern bottom slope of the South YS and fast southward movement of the YS Cold Water Mass. Further numerical experiments indicated that the magnitudes of the above changes increased with increasing maximum wind speeds and/or decreasing moving speeds of typhoons.