孟加拉湾表层盐度季节变化和ENSO循环的拓展伴随模态分析

IOCAS-IR > 海洋环流与波动重点实验室

	孟加拉湾表层盐度季节变化和ENSO循环的拓展伴随模态分析
其他题名	Extended Associate Pattern Analysis on the Evolution of Sea Surface Salinity in the Bay of Bengal and ENSO Cycle
	吴玲娟
学位类型	博士
	2007-06-15
学位授予单位	中国科学院海洋研究所
学位授予地点	海洋研究所
关键词	拓展伴随模态分析、淡水羽、盐度锋面、季节变化、enso
摘要	本文采用旋转经验正交函数分析和拓展伴随模态分析方法研究孟加拉湾表层盐度的季节变化，结果表明其主要特征是西北淡水羽（位于湾的西北部）和东北淡水羽（位于湾的东北部）的季节性演变。西北淡水羽始于7月初，8月底达到峰值，10月底转变为湾形淡水羽；湾形淡水羽集中分布在孟加拉湾的西北和东北沿岸附近，并在第2年1月转变为东北淡水羽。孟加拉湾北部的环流（地转流+Ekman漂流）对淡水羽的形成和演变起重要作用。Sverdrup环流，代表对风应力的正压响应，能部分解释除了秋季湾形淡水羽的东支之外淡水羽的形成机制和演变过程。海表淡水通量与淡水羽在空间上分布不一致：当孟加拉湾东北部的海表淡水通量急剧增加（减少）时，西北淡水羽（湾形淡水羽的东支）产生，所以海表淡水通量不是淡水羽的形成和演变的主要原因。此外，孟加拉湾周边河流的径流量可能只是淡水羽的主要淡水来源，而与淡水羽的形成和演变关系不大。初步研究了孟加拉湾北部盐度对海面高度异常的影响，结果表明Ekman 抽吸对孟加拉湾的海面高度异常起着主要作用，热量通量和淡水通量起次要作用。7－12月，孟加拉湾北部的淡水通量决定北部的海面比容高度异常；1－3月，热量通量对海面比容高度异常起主要作用；4－6 月，热量通量和淡水通量在不同时空对孟加拉湾北部的海面比容高度异常起不同的作用。同样，采用拓展伴随模态分析方法研究ENSO循环的暖位相——El Niño，表明必须将中低纬度印度洋和太平洋海气系统作为一个整体来研究El Niño；证实了正是直接来自南北中纬度太平洋的异常西风爆发和海面风辐聚所驱动的近赤道异常表层海水东移和经向辐聚，而不是Kelvin波，造就了El Niño现象的增温信号。El Niño事件中海洋和大气具有明显不同的性态：气候系统中并不存在一个相对独立的热带太平洋大气变异，但是的确存在一个相对独立的热带太平洋海洋变异。总体上而言：El Niño事件早期主要是大气驱动海洋，晚期主要是海洋驱动大气。研究结果显示拓展伴随模态分析方法是研究ENSO循环和海洋水文特征形成机制的有力工具。
其他摘要	The evolution of sea surface salinity (SSS) in the bay is studied using Rotated Empirical Orthogonal Function (REOF) analysis and Extended Associate Pattern Analysis (EAPA). The results show that SSS distribution in the northern bay is featured by eastern-bay and western-bay plumes in the northern bay during different seasons. The western-bay plume begins in early July, peaks in late August, turns into a bay-shaped plume with the two plumes in either side of the bay in late October. The southward extension of the western-bay plume is explained by the southwestward geostrophic flow associated with the cyclonic gyre in the northern bay, which counters the northeastward Ekman drift driven by wind stress. The offshore expansion of the western-bay plume is induced by the offshore Ekman drift which also produces a nearshore salinity front. The bay-shaped plume appears when the cyclonic gyre shifts westward and a weak anticyclonic gyre occupies the northeastern bay. As season advances, the western part of the bay-shaped plume decays while the eastern part persists until next June, which is believed to be associated with the anticyclonic gyre in the northern bay. The circulation of the plumes throughout the year except the eastern part of bay-shaped plume in fall can be partly explained by the seasonal variation of mass transport associated with the Sverdrup balance. The western-bay (eastern-bay) plume appears when surface freshwater flux in the northeastern bay increases (decreases) dramatically, which imply that the plumes are not directly produced by surface freshwater flux. River discharge seems to be the freshwater source for the plumes and has little to do with the evolution of the plumes. Similarly, EAPA is adopted to study the formation mechanism of warm phase of ENSO cycle—El Niño. The results show that El Niño events mean a redistribution of sea surface temperature (SST) covering almost the whole Pacific, which needs a huge amount of energy provided by the air-sea interaction over the Pacific and related regions; It confirms that it is the westerly burst and wind convergence, coming directly from middle latitudes, instead of Kelvin waves, that produce the strong SST warm signal in Nino regions. The results also show that the air and sea behaviors that induce El Niño are quite different. There does not exist a relatively independent tropical atmosphere but does exist a relatively independent tropical Pacific because the atmosphere is heated from the bottom instead of the surface, leading to much stronger baroclinic instability than the ocean and has a very large inter-tropical convergence zone covering the most tropical Pacific. In general, the ocean is forced by the atmosphere during the early stage of El Niño events, while the atmosphere is forced by the ocean during its late stage. The results show that EAPA is effective tool for studing the formation mechanism of oceanic hydrography and ENSO.
页数	90
语种	中文
文献类型	学位论文
条目标识符	http://ir.qdio.ac.cn/handle/337002/655
专题	海洋环流与波动重点实验室
推荐引用方式 GB/T 7714	吴玲娟. 孟加拉湾表层盐度季节变化和ENSO循环的拓展伴随模态分析[D]. 海洋研究所. 中国科学院海洋研究所,2007.

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