Study On The Effect Of Gale And Ocean Eddy On Chinese Offshore Water Exchange In Winter

Water exchange between different sea areas can promote the exchange of marine materials and the dilution of marine pollutants, which has a very important role in the purification of the marine environment. The marine dynamic environment of coastal waters of China is simulated by using the ROMS marine numerical model. An improved spectral mixture model method(SMM) is quoted, and the problems of water exchange between the Bohai and Yellow Seas are discussed. On this basis, the influence of gale on the water exchange between the Bohai and the Yellow seas and ocean eddy on the water exchange between the Kuroshio and the East Sea are investigated.1. The definition and characteristic of the water exchange zone between the Bohai and Yellow seas.The marine dynamic environment of the Bohai and Yellow Seas in the winter of 2006 is simulated by using the ROMS marine numerical model.On the basis of the simulation results of temperature and salt, the water mass in the research region is analyzed by an improved spectral mixturemodel method and the water exchange zone is defined. It has been found from the study that there are the Bohai Sea water mass in low temperature and the Yellow Sea water mass in high temperature in this area in winter.And the Yellow Sea water masses are distributed in the shape of “tongue”in the north of the Bohai strait region, with a tendency of running from northwest to southeast, and the area of water exchange is maximum at the tip of the “tongue”. Besides, by further narrowing the scope of the study, it is also found that the coastal area in the northernmost Yellow Sea does’ t participate in the water exchange between the Bohai and Yellow Seas.2. The effect of winter gale on the water exchange zone between the Bohai and Yellow Seas.Based on the the variation trend of the wind speed in the Bohai and Yellow Seas area in winter with time, a gale event(February 14, 2007) is found. Take the gale event as an example, the change of water exchange zone between the Bohai and Yellow Seas before and after the gale as well as in the process of the gale is discussed. The study says that the winter gale events play a role in promoting the water exchange between the Bohai and Yellow Seas. It is specifically shown by the fact: the Yellow Sea warm current invades the Bohai Sea further under the influence of the gale process; The water exchange zone extends in the direction of the Bohai Sea;The water exchange zone in the southern part becomes wider; The mixture zone of river runoff with the Bohai Sea water upon its entry into the Bohai sea is enlarged and shifts northwards. Within two days after the gale, the exchange zone in the strait area retreats toward the Yellow Sea and the exchange zone resulted from the Yellow River runoff also shrinks back towards the coast.3. The abnormal distribution of the onshore transport volume across the 200 isobath in winter during 1991-2006.The marine dynamic environment of the East Sea during 1991-2006 is simulated by using the ROMS marine numerical model. On the basis of the simulation results, the abnormal distribution of the onshore transport volume across the 200 isobath in winter during 1991-2006 is analyzed. And the mean flow fields when he onshore transport volume across the 200 isobath in winter is normal and abnormal are further explored separately.The study says that the water volume fluxes in 1997, 2003 and 2004 are abnormally high, especially, which in 1997 is the highest. At the same time,the water exchange capacity between the Kuroshio and the East Sea is relatively weak. And the section of the Kuroshio in the east of Taiwan shifts away from the the East Sea shelf. In addition, the water volume fluxes in2000, 2002 and 2005 are abnormally low, especially, which in 2000 is thelowest. At the same time, the water exchange capacity between the Kuroshio and the East Sea relatively strengthens. And the Kuroshio invades the East Sea from the northeast of Taiwan further.4. The movement character of the eddy in the East Sea in winter of1997 and 2000.The abnormal distribution and the movement character of the eddy in the East Sea in winter of 1997 and 2000 are explored. It is found from the study that the water volume fluxes in 1997 is the highest. Meanwhile, the cyclonic eddies in the west of the Kuroshio bear to the Kuroshio along the southwest from the East Sea. So the area of water exchange zone between the Kuroshio and the East Sea decreases and its capacity weakens. In addition, the water volume fluxes in 2000 is the lowest. Meanwhile, the cyclonic eddies in the northeast of Taiwan are not apparent. And the cyclonic eddies in the west of the Kuroshio bear to the East Sea along the northwest from the Kuroshio. So the area of water exchange zone between the Kuroshio and the East Sea increases and its capacity strengthens.What’s more, the study also finds that the generation of the eddy in the East Sea is associated with ENSO.5. The influence of ocean eddy on the water exchange between the Kuroshio and the East Sea.On the basis of the analysis result data of mesoscale eddy in the global ocean, the eddies of the East Sea are identified and tracked and its temporal and spatial distributions are analyzed. And the relationship between the temporal and spatial distributions of eddy of the East Sea and the onshore transport volume across the 200 isobath in winter is further discussed. The results and conclusions are described in detail as follows.The eddies are relatively frequent in the bending region where the Kuroshio to the East Sea. When the eddies of the East Sea are located in the area where from the west of the middle section of the Kuroshio axis to the south of chejus Island which is in the northwest of Ryukyu Islands, it is favorable to the water exchange between the Kuroshio and the East Sea.Moreover, the eddies which is situated in the west of the Kuroshio axis from the Kuroshio moves to The East Sea along the northwest direction can weaken the onshore transport volume across the 200 isobath and promote water exchange between the Kuroshio and the East Sea. Finally, through the number statistics of eddies, it is found that the more cyclonic eddy in the East Sea can much more promote the water exchange capacity.