Primary analysis of current condition and seasonal variation in southern Zhejiang

To research the current character,seasonal variation and pattern in vertical profile,vertical current speed and direction were observed using ADP,in summer,winter,spring and autumn from 2006 to 2007,in a fixed site of east China Sea southern Zhejiang Province. The results show: (1) The biggest speed was 148.9 cm/s,with the direction 75°,occurred in spring ebb peak in spring during the four observation periods. The biggest average speed in vertical reached 106.2 cm/s,occurred in spring ebb peak in summer. (2) Significant difference presented in vertical speed profile. In the surface (above 28 m),the current was interfered evidently by sea conditions with the biggest and least average speed in autumn and in winter,respectively; between 20m and 28 m layers,the current was strongest in winter and least in spring season; while below 20 m layer,the current was strongest in summer. The average speed in vertical profile was strongest in summer and least in spring,with the speed of 46.5 cm/s and 33.7 cm/s,respectively. (3) The current direction varied from season to season. In summer the direction was north,while in autumn and winter was south on the whole. However,in spring the current was periodic alternating,and the north current was dominated. (4) In vertical profile the current direction was consistent in every layer,while in winter and autumn the current direction varied clearly from bottom to surface. (5) In vertical profile the average residual flow speed was 12.8~29.8 cm/s in the four seasons and the residual flow was strongest in summer and least in spring. The direction of residual flow in summer and spring was northeast in every layer,in winter the direction was southwest. However in autumn the flow direction was complicated relatively,11 m above the seabed was east to north-east-east and below 11m layer the direction was southwest. Conclusion: In the study area,the current was controlled by tide,monsoon and Taiwan warm current together. The monsoon influence to the current in summer and winter was stronger than in spring and autumn,meanwhile the influence became weaker from surface to bottom.