Observation And Analysis Of The Coastal Current And Its Adjacent Current System In The China Offshore Waters

The waters covered by the coastal current is the focus waters of the marine development and protection of the China coastal provinces. Deepening the scientific understanding of the China offshore coastal current and its adjacent current system not only has the important meaning of the physical oceanography, can also provide the strong foundation to support for the marine dynamic process of the biology, chemistry, ecology. Meanwhile, it provides a scientific decision basis for our nation to the environmental protection, development and management of the coastal waters. Based on the abundant data including the salinity measured by CTDs and current by the seabed and mooring systems in four seasons from 2006 to 2007, the history salinity, Argos drifter trajectory and MODIS water color, this article systematically analyzes the distribution features and seasonal variations of the coastal current and its adjacent current system in the China offshore waters, and focus on inquiring into the several problems, such as the Lubei coastal current and the water exchange through the Bohai strait, the summer and winter circulation off the Qingdao coast, the composition and whereabouts of the Subei coastal water, reversing process of the South China Sea western boundary current. This study gets the significant progresses as follows:1) the seasonal variation of the Lubei coastal water and coastal currentIn autumn and winter, the Lubei coastal water flows out of the Bohai strait along the coast, then continues to travel eastward,finally goes southward to arrive the Shandong peninsula eastern waters around the Chengshantou. During the prosperous period, the coastal water with low salinity can go further southward to the Shidao waters about 35.5°N. In spring, the coastal water in the southern Bohai Sea can’t flow out of the Bohai strait. The coastal water from the east of Penglai to the Shidao waters should be the residual coastal water in winter, which continues to travel eastward driven by the cyclonic circulation in the northern Yellow sea. In summer, the surface water in the Bohai Sea flows out from the Bohai strait.2) Three patters of the water exchange between the Bohai Sea and Yellow SeaThe first pattern is "the inflow in the north and outflow in the south of the Bohai Strait", i.e., in winter the water in the northern Yellow Sea flows into the Bohai Sea through the Lao-tie-shan channel while the water in the Bohai Sea flows out via the Dengzhou channel, and the inflow is slightly greater than the outflow. The second pattern is "the outflow in the upper layer and inflow in the bottom layer of the Bohai Strait" in summer, which is on the contrary to the winter, but the outflow is significantly greater than the inflows due to the increase of the runoff and precipitation. The third is the unbalanced seasonal water exchange in spring or autumn. In spring, the low mean sea level and the north-southward sea level incline in the Bohai Sea in winter lose the dynamic balance due to the northeast monsoon reversing, which force the water in the northern Yellow Sea into the Bohai Sea through the south and north channels.The net inflows is the largest of the four seasons. In autumn, it is "the inflow in the north and the outflow in the south of the Bohai Strait", and the outflow is more than the inflow, the net outflow volume is much smaller than the net inflow in spring.3) The residual current off the Qingdao coast is the results of the wind and the Shandong peninsula topography. In summer, the surface current is the superposition of the northward Ekman flow driven by the south wind and the cold water mass circulation off the Qingdao coast. The surface current flows to the north when the south wind is strong, and the current is controlled by the cold water mass circulation in the middle layer. In autumn and winter, southward and northward surface current (i.e., offshore and onshore flows) occur alternately, and the offshore surface current is obviously stronger than the onshore current. The northward flow in the bottom holds obvious advantage, which belongs to a compensation current. In spring, the monsoon gradually reverses into the southward from northeastward, the surface flow shows the onshore and offshore flows alternately, but the bottom flow is very small.4) Driven by the northeast monsoon in winter,the Subei coastal water is southward along the coast, and turns to southeast into the East China sea after leaving the Subei shoal. In summer, the Subei coastal water with low salinity flows out the shoal area through the tide current troughs, where the coastal water mainly has three branches:first and second branches flow eastward from Jianggang and Sheyang estuary respectively, eventually leave the shoal and enter the surface circulation in the southern Yellow Sea in summer; Third branch flows northward into the Haizhou bay started from the Guanhe estuary, and eventually enters the summer ocean circulation off the Qingdao coast. In summer, the northward Ekman current is stronger than the cold water mass circulation, when the south wind is strong. This causes an intermittent northward surface current in the offshore area from Haizhou bay to Rizhao. Basing on the salinity distribution in the Subei shoal area in winter and summer, we estimate the contribution of the runoff entering the Subei shoal area in the salinity balance, whose result shows it is necessary that the Changjiang diluted water flows northward into the Subei coastal waters. Moreover, the pathway northward into the Subei shoal area abuts onto the Qidong coastline shown by the measured salinity.5) In summer, the Yuedong coastal water is stronger. It has an eastward branch near the Shantou waters, which flows along the south side of the Taiwan shoal, then enters the Penghu channel, and flows to the north. Meanwhile, the Yuexi coastal water is limited in the area from the Zhujiang estuary to Yangxi, and the coastal area west to Yangxi is occupied by the outer sea water driven by the cyclonic circulation.6) To clarify the reversing process of the south China sea western boundary currentUsing the merged sea level anomaly and the absolute geostrophic velocity products obtained from the satellite altimetry data as well as the Argos drifter data, we analyze the reversing process of the South China Sea western boundary current (SCSwbc) from summer-model pattern to winter pattern and the important oceanic phenomena occurring during this process. Results show that outbreak time of the northeast monsoon over the southern SCS lags about one month behind that over the northern SCS. In the SCS monsoon revering period, the SCSwbc reveres also rapidly into the winter-pattern at the Guangdong continental slope in late September, and following this, the southward Vietnam coastal boundary current (VCBC) strengthens. However, the northward Natuna current still keeps a summer state until the middle of October.Thus the balance between the two of southward and northward currents lose when they meet, so their meeting position goes gradually toward the south. However, the main stream of the Vietnam off-shore Current (VOC) keeps basically near the original latitude, so that a loop current is formed in the southeast of the Vietnam. In this period, the VOC and its associated dipole circulation system become strong. After the middle of October, the northward Natuna Current starts to weaken, the loop current sheds at last and becomes a cool ring. Meanwhile, the VOC and its associated dipole sub-basin circulation system also weaken gradually, until disappears. Analyzing results indicated also that the responses of the western boundary current to the northeast monsoon are different in the three segment regions including the Guangdong continental slop, the southwestern continental slop, the middle area。...