Typhoon-induced variation of semidiurnal internal tides along the southeastern coast of Korea

Typhoon-induced strong winds can change the oceanic environments dramatically, which sometimes damage the fisheries and power plants located along the coast. In July 2015, two consecutive typhoons, Chanhom and Nangka, passed over the Yellow and East/Japan Seas within a week. The temperature observed near the southeastern coast of Korea fluctuates with the typhoon-induced upwelling and downwelling events interrupting the typical stratification condition. In addition, the energy of semidiurnal internal tides from observed temperature and current data variates depending on changes of stratification condition. Data-assimilated numerical simulation results reveal that the generation of semidiurnal internal tide energy from a region north of the Tsushima Island is dependent on the barotropic tides. However, during the typhoon-induced downwelling event, the energy of semidiurnal internal tides near the southeastern coast of Korea varies much different from the barotropic tidal forcing. The sloped pycnocline near the southeastern coast in the typical condition enables the internal tidal energy to be transmitted toward a shallow region from the generated region. The downwelling event deepens the pycnocline and makes the internal tide energy reflected and concentrated in the adjacent sea. This result presents a case study showing that typhoon-induced stratification changes can modify propagation of internal tides, which charge a large portion of the ocean mixing processes.