The Study on Upper Ocean Responses to Typhoon Cimaron and Eddy Heat Flux in the South China Sea

This dissertation focuses on the investigation of the upper ocean response to typhoon Cimaron (2006) and annual variations of horizontal eddy fluxes in the South China Sea (SCS) through the methods both of satellite remote sensing and numerical ocean modeling.;The mixed layer deepening induced by typhoon Cimaron is derived based on satellite observed sea surface temperature (SST) and climatological temperature profiles in the SCS. Corresponding to the SST drop of 4.4 °C on November 3, 2006, the mixed-layer deepened by 104.5 m relative to the undisturbed depth of 43.2 m, which is consistent with the simulation results from the one-dimensional mixed-layer model (GOTM). Furthermore, baroclinic geostrophic velocity and vorticity are calculated from the surface temperature gradient caused by the typhoon. The negative vorticity, associated with the typhoon cooling, indicated an anti-cyclonic baroclinic circulation strongest at the base of the mixed-layer, and at the depth of 50 m, the geostrophic speed reached as high as 0.2 m s -1. Typhoon Cimaron proceeded slowly (1.7 m s-1) when it was making a southwestward turn on November 3, 2006, resulting in a subcritical condition with a Froude number (the ratio of typhoon translation speed to first baroclinic mode speed) of 0.6 around the maximum SST drop location and facilitating high SST cooling and mixed-layer deepening due to absence of inertial-gravity waves in the wake of the typhoon. Comparison of Argo buoy data with the climatological temperature suggests that the average uncertainty in the mixed-layer deepening estimation caused by the difference between Argo and climatological temperature profiles is less than 10 m.;The physical dynamic and biological responses to typhoon Cimaron are investigated through a three-dimensional ocean model, the Regional Ocean Modeling System (ROMS). The correlation between simulated sea surface temperature (SST) and the satellite observations is over 84%, which indicates ROMS can generally simulate the sea surface temperature in the South China Sea during typhoon process. However, detailed analysis shows that the ROMS model underestimates the sea surface temperature cooling and mixed layer deepening because of insufficient mixing in the modeling. The wave-induced mixing term (Bv) added into the nonlocal K-Profile Parameterization (KPP) scheme can increase the simulation accuracy of surface temperature cooling and mixed layer depth deepening in response to the typhoon forcing. The simulation results show that the blooming of phytoplankton in the wake of storm appeared one week later after typhoon's passage. The concentration of chlorophyll is 0.1 mg m-3 at pre-typhoon time and increase to 1.9 mg m-3 on November 9. Satellite Observation indicates the concentration of chlorophyll in wake of typhoon Cimaron was also in a high value of 0.85 mg m-3 on November.;The eddy heat flux in the SCS is derived from the satellite data including the altimeter surface height anomalies and optimally interpolated sea surface temperature. The long term heat flux shows a northward heat transport on the west side of the SCS, comparable to that in other strong flux regions such as the Kuroshio extension. The eddy flux becomes the strongest in winter with the inflow flux in the south and the outflow through the Luzon, and the eddy heat can flux through the Taiwan Strait into the East China Sea. The convergence of the flux indicates that heat accumulation in the eastern SCS close to Luzon Strait in winter and also to southeast of Vietnam in winter and summer. The eddy heat flux is more significant in adjusting the ocean upper layer heat budget flux in winter and summer.