Bottom layer temperature and Sea Surfave Height during the Typhoon Lekima

Direct observations and a high-resolution ocean model were used to investigate the significant bottom temperature response in the north Yellow Sea (NYS) during weakening and dissipation of typhoon Lekima in August 2019. Strong cyclonic circulation with eastward currents along the southern coast and westward currents along the northern coast of the NYS was generated by the cyclonic typhoon wind. Meanwhile, high sea level occurred along the northern coast of Shandong Peninsula and southern coast of Liaodong Peninsula. Low sea level existed between the northern and southern coast of the NYS. Momentum balance analysis showed that this sea level pattern that lasted for a weak after the typhoon’s dissipation, maintained the eastward currents along the southern coast and westward currents along the northern coast of the NYS in geostrophic balance to the lowest order. The persistent eastward alongshore current drove warm bottom water eastward along the northern coast of Shandong Peninsula, causing significant bottom temperature warming up to 11°C. At the same time, the westward alongshore current transported cold water from region near the YSCWM westward along the southern coast of the Liaodong Peninsula, leading prominent bottom temperature cooling up to 13°C. Temperature budget analysis further confirmed the leading role of horizontal temperature advection related to typhoon induced alongshore currents in the dramatic bottom temperature anomalies. Near-inertial oscillations also disturbed the thermocline and provided favorable condition for the eastward advection of bottom warm water. This study highlights the importance of weaker synoptic weather system instead of strong typhoons on the sharp bottom temperature variations around the coastal regions.