The Diagnostic Calculation Of Circulation In The South China Sea

This article adopted the method of P-vector to calculate the South China Sea circulation and gyre system which is corresponding to the sequence of temperature and salt data provided by Professor Lan Jian and obtained the conclusions as followed which are divided into two parts . Firstly , it was concluded on the basis of seasons.lThe whole surface of the South China Sea is controlled by a large cyclonic circulation in winter, among which there is a medium-size closed circulation in the north and the south respectively and a small anti-cyclonic circulation between them. There is basically a large cyclonic circulation system in the middle north area. In the east coastal area of Guangdong and the deep water of Guangdong external sea , there is a South China Sea Warm Current flowing quite invariably towards the northeast direction. There is a cyclonic gyre respectively in the northwest area of Luzon and to the east of Vietnam . In the Xisha-Zhongsha islands area ,there is a anti-cyclonic gyre . In the southwest coastal area of Palawan , there is a anti-cyclonic circulation .In the vicinity of Bashi Channel ,owing to northeast monsoon prevailing in the north South China sea and the west Pacific , it is favorable for the Kuroshio to flow into the South China Sea with basically northwest direction.2 In spring , the wind field of the sea surface is in the changing period and its direction is variable .As analyzed .comparing with the surface circulation in winter , the flowing state of it in spring changes greatly. In winter ,the overall tendency of surface cycloniccirculation in the South China Sea seems to disappear. A local cyclonic circulation system only forms in the north South China Sea which is to the north of 1600N. The strength of cyclonic circulation in the northwest Luzon and in the east Vietnam apparently becomes weaker .The anti-cyclonic circulation in the coastal area of the southwest Palawan seems to exist no more. However .there is an anti-cyclonic gyre system and a cyclonic gyre system respectively in the offing and the external sea of the southeast Vietnam.3The southwest monsoon flows in summer . Its surface circulation state is almost opposite to the state in winter .which is flowing in the northeast direction in most sea area. In summer , the flowing tendency of northeast direction prevails absolutely in the middle South China Sea especially the northern part .whereas a large anti-cyclonic circulation appears in the southern part . In summer , the several obvious local circulation on the surface are all located in the western half of the South China Sea :the center of the Luzon Cool Gyre in the northwest Luzon in winter moves to the position of 1800N 11600E,the strength and the range grows weaker and smaller than winter; there are two anti-cyclonic gyre in the southeast Vietnam. In the vicinity of Bashi Channel , when the surface Kuroshio flows to the eastern side of the channel in summer ,being blocked by the current of the north South China Sea flowing in the northeast direction ,it turns to the northeast and converges into the main stream of the Kuroshio after it enters in the middle of the channel . It seems that it doesn' t enter the South China Sea . In the south Bashi Channel ,since the current flowing in the northeast direction flows out of the channel , it forms a local cyclonic cool gyre with the Kuroshio in the east and middle channel. We can see from Figure 5 that the current flowing in the northeast direction at the western side of the Bashi Channel is originated from the external sea ofJinlan gulf .Being related to the several local circulation in the western half of' the South China Sea above mentioned ,it continues flowing in the northeast direction and straight to the Bashi channel after it passes the Zhongsha islands. It can be considered that the strength of the current and the circumstance whether the Kuroshio can enter into the South China Sea is closely connected.4In autumn , the southwest monsoon subsidizes quickly Subsequently ,the surface drift flowing in the northea...