长江口外海域冬、春季水温变化规律研究

收集了1963—1996年长江口外海域水温的观测数据,分析了该海域冬、春季表层、10m层、20m层和30m层不同层次水温的季节和年际变化规律,以及其间水温垂向结构的变化。季节变化上,表层多年平均水温在8月最高,3月最低,底层多年平均水温9月最高,3月最低。年际变化上,冬季在1979年存在一个由冷到暖的跃迁;4月水温的年际变化较冬季复杂,表层、10m层、20m层和30m层水温分别在1979、1973、1973和1975年发生从冷到暖的跃迁。水平分布上,冬季除东南角小范围表层水温降低外,沿岸及北部海区表层水温均升高,春季北部和南部中间海域水温升高,升温幅度由表层至30m层逐渐变小。垂向结构上,冬季表底混合均匀,表层与20m层的年际变化相关系数高达0.97,春季表层与20m层的水温差存在10年左右的变化周期。本文将一些可能影响春季水温年际变化的因素与海温进行了比较并发现,在冷期,春季表层海温与长江口外海域气温相关较暖期好,相关指数为0.79;而暖期的春季表层与20m层的水温差与净热通量相关系数较高,为0.65。

VARIATIONS OF THE WATER TEMPERATURE OFFSHORE THE CHANGJIANG RIVER ESTUARY IN WINTERS AND SPRINGS

Using historical water temperature data offshore the Changjiang River estuary from 1963 to 1996, we analyzed seasonal and inter-annual temperature variations at sea surface, 10m, 20m and 30m depths and the variations of vertical structure. Seasonally, we found that the surface water temperature was the highest in August and the lowest in March; the bottom water temperature was the highest in September and the lowest in March. For inter-annual variations, the winter water temperatures shifted from cold phase to warm phase in 1979. Although the spring (defined as April here) water temperatures at all depths also shifted from cold phase to warm phase. The shifts occurred in different years. Horizontally, the winter surface water temperature had an increasing trend along coast and northern part of study area but a decreasing trend on southeastern part; spring water temperature had an increasing trend, whose magnitude decreased from sea surface to 30m depth, in northern and middle-southern areas. Vertically, winter water temperatures were homogenous and the correlation coefficient for inter-annual variations between sea surface and 20m depth was 0.97; water temperature difference of sea surface and 20m depth in spring presented an approximately 10 years periodic variation. We examined some possible factors affecting inter-annual variations in water temperature in spring and found significant correlation between sea surface water temperature and air temperature during cold period and the correlation coefficient was 0.79, which was greater than that during warm period. We also found significant correlation between net heat flux and water temperature difference of sea surface and 20m depth during warm period, with a correlation coefficient of 0.65.