Kuroshio In The East China Sea Surface Instability In The Process Of Remote Sensing And Numerical Simulation Study

The Kuroshio frontal instable processes (KFIP) in the East China Sea (ECS) not only have a great impact on the hydrologic characteristics, the pollutants drift, the distribution of seafloor sediment and the ships navigation of the ECS, but also are closely related to the climate changes of the coastal areas of the ECS. However the frequency and area of occurrence of the KFIP have not been studied fully and detailedly.In this study, remote sensing observation and numerical modeling were used to study the space-time character of the the KFIP when they arising and evoluting.On the remote sensing observation, level 2 data of MODIS SST and Kd490 ranging from July 1, 2002 to June 30, 2009 of the ECS when there was no cloud impact or little were selected. By using of the data, the minimum standards of the Kuroshio temperature front and the diffuse attenuation coefficient (Kd490) front of the ECS are given. Based on these standards and the curvature distinguish methods (CDM), the standard of curvature distinguish for the KFIP in the ECS are put forward. By making use of this standard, we study a total of 2073 satellite-derived images, and discover that as long as there is no cloud impact from January to May and October to December, the KFIP in the ECS are surely found in MODIS satellite images. From June to September, the frequency of occurrence can also reach to 82.9% at least. Moreover, it is obtained that there are three source regions of these instability processes, namely, (26oN,121.5oE) nearby, (27oN, 125oE) nearby and (30oN, 128oE) nearby. The differences of the characteristics of these instability processes which are generated in different regions are analyzed in the present study.For the Kuroshio frontal instability processes of East China Sea, the width is comparatively large while the amplitude is comparatively small in the rising at the source regions; after they move together with the Kuroshio mainstreams, the width gradually becomes smaller while the amplitude gradually becomes larger; eventually, they either integrate into the next instability processes, or disappear at the shelves. When Kuroshio frontal instability processes of East China Sea move from 27 o N to 30 o N with Kuroshio mainstreams, the speed reduces from the average of 46.5cm/s to the average of 29.4cm/s.For the KFIP in the East China Sea, the width is comparatively large while the amplitude is comparatively small in the rising at the source regions; after they move together with the Kuroshio mainstreams, the width gradually becomes smaller while the amplitude gradually becomes larger; eventually, they either integrate into the next instability processes, or disappear at the shelves. When Kuroshio frontal instability processes of East China Sea move from 27oN to 30oN with Kuroshio mainstreams, the speed reduces gradually.The second part, liner and nonlinear numerical models are used. The spectral method as the numerical formulation is applied in the liner mumertical modeling, the factual submarine topography is selected and the suitable basic state is used to solve the problem. The first two most unstable modes are found. The wavelength correspondging to the most unstable waves and the occurrence position of the most unstable waves are obtained at the same time. The HYbrid Coordinate Ocean Model or HYCOM is used in the nonlinear numerical assimulation, and the two important conclusions are obtained. First of all, the KFIP occur in summer also, which offset the MODIS's shortage in detection the KFIP in summer. So we can draw a conclusion thar the KFIP always exist in the East Chind Sea all year. Secondly, the period of the Kuroshio frontal instability process of northeast Diaoyu Islands and southwest Yakushima is about 14 days and 20 days respectively.