Characteristic of the thermal structure of upper layer after a typhoon passage in the East China Sea

Abstract

Four Autonomous Drifting Ocean Station (ADOS) drifters with temperature and pressure sensors and two Acoustic Doppler Current Profilers (ADCPs) were deployed to observe thermal structure of the Kuroshio branch current in the East China Sea at the August in 2007. During the experiment a typhoon closely passed the study area and distinct typhoon signals are detected by the equipments. Immediately after the typhoon passage, sea surface temperature (SST)abruptly dropped down from 28°C to 24°C and thermocline, had existed between 30~50 m depth before the typhoon passage, disappeared with the strong vertical disturbance. It is maintained over five days after a typhoon passing. The inertia oscillation is detected in drifter trajectories after the typhoon passage. Vertical oscillation by inertial wave with about 24 hours period is showed up very strongly for 4 or 5 days after the typhoon passing. In that period, the strong vertical shear of horizontal current component is analyzed in the drifters and ADCPs, even though the vertical temperature gradient is relatively mild. The vertical current shear is mainly induced by phase difference of clock-wise rotating inertia component. After a typhoon passage, the internal inertia oscillation with weak vertical stratification can activate supply of nutrients from the bottom layer to the euphotic zone and primary production in a shelf area. The vertical material transport and ecological processes after the typhoon passage in the East China Sea will be the future work.