Variability of the Kuroshio in the East China Sea and the currents east of Ryukyu Islands Ⅰ. Variability of the Kuroshio in the East China Sea and the meso-scale eddies near the Kuroshio in 2000

On the basis of hydrographic data obtained in 5 cruises of 2000 onboad the R/V Chofu Maru and the QuikSCAT wind data during 5 cruises of 2000,the velo city and volume transport (VT) of the Kuroshio in the East China Sea (ECS) are computed by using the modified inverse method.The following main results have been obtained.(1) The wind speeds and wind-driver currents both are strongest in January February among 5 cruises of 2000,and the directions of wind-driver current are northward only in July of 2000,which streng then the Kuroshio current in the ECS.(2) The lowest value of salinity at the surface is minimalin summer,and the lowest value of salinity at the surface is maximal in January-February.This means that the Changjiang River discharge diffuses northeastw ard at the surface layer in summer,but it diffuses southward at the surface layer in winter.(3) The current structure and its variations at Section PN in 5 cruises of 2000 are as follows.The Kuroshio at Section PN has two current cores in January February,October and November,and only one current core in April and July,respectively.The main axis of Kuroshio is located at the computational point 9 of Section PN in January February,and at the computational point 8 of Section PN,which moves toward the shelf,in other months,respectively.(4) The Kuroshio through Section T K has multi-current cores during 5 cruises of 2000.The main current core of Kuro-shio occurs only at the computational point 8,whose water depth is greater than 1 200 m,in November,and occurs at the computational point 2 or 4,whose water depth is less than the 400 m levels,in other months,respectively.(5) The net northeastward volume transport through Section PN is maximal,28.1×106 m³/s,in November among 5 cruises of 2000,and is next in July,and is minimal,24.6×106 m³/s,in October among 5 cruises of 2000.The annual average of its net northeast ward VT is 26.4×106 m³/s in 2000.(6) The week cyclonic eddy occurs only in November and in area east of the Kuroshio at Section PN.But an anticy clonic and warm eddy occurs in area east of the Kuroshio at Section PN in other months,especially,is strongest in October.When an anticyclonic and warm eddy east of the Kuroshio strengthens,the VT of Kuroshio seems to decrease,such as in October.Inversely,when an anticy clonic and warm eddy east of the Kuroshioi is week,such as in July,or when the cyclonic eddy occurs east of the Kuroshioi,the VT of Kuroshio seems to increase,such as in November.In comparison of the current patterns of the circulation in October and November in the ECS,their variations of the circulation are greater in the ECS.This shows also that the interaction between the Kuroshioi and meso-scale eddies near the Kuroshio is important.(7) The net eastward VT through Section TK is maximal also in November among 5 cruises of 2000,and is next in July,and is minimal in October and January February among 5 cruises of 2000.Its annual average net eastward VT through Section TK is 21.9×106 m³/s in 2000.(8) The net northward VT through Section A is maximal,3.5 and 3.1×106 m³/s,in January-February and April,respectively,and is minimalin July among 5 cruises of 2000.Its annual aver age net northward VT through Section A is 2.7×106 m³/s in 2000.This means that the VT of the Tsushima Current is maximal in January February and April,and is minimal in July among 5 cruises of 2000.