若干大洋西边界潜流的分布特征及其形成机制

IOCAS-IR > 海洋环流与波动重点实验室

	若干大洋西边界潜流的分布特征及其形成机制
其他题名	The distributing of several western boundary undercurrents and the correspongding dynamic mechanism
	臧楠
学位类型	博士
	2008-06-14
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	西边界潜流温跃层太平洋印度洋
摘要	大洋环流是海盆尺度上海水的持久流动，是海洋中质量、热量输运的主要通道，对全球气候变化有重要影响。经过二十年来的大量调查研究，对海洋上层的风生大洋环流有了比较充分的认识。然而，近几十年来的大量观测显示，大洋环流的垂直结构并非像传统认识的那样单一，在很多区域存在与之反向的次表层潜流，如北赤道流（NEC）下方的北赤道逆流（NEUC）、棉兰老海流（MC）下方的棉兰老潜流（MUC），吕宋岛附近黑潮（KC）下方的吕宋潜流（LUC），东澳大利亚海流（EAC）下方的大堡礁潜流（GBRUC）和东澳大利亚潜流（EAUC），阿加勒斯海流（AC）下方的阿加勒斯潜流（AUC）等。这些潜流一般分布在西边界，或者在西边界处增强，称为“西边界潜流（WBUC）”。与表层环流相比，对次表层潜流的结构和形成机制认识不足，因此利用不断更新的各种实测数据和高分辨率同化数据，通过理论分析和数值试验，探讨研究次表层潜流的分布特征和形成机制，对于大洋环流动力学理论的进一步发展具有重要的科学意义。本文利用中国ARGO资料中心提供的ARGO资料、全球简单海洋资料同化分析系统产生的SODA同化资料和日本地球模拟器模拟出来的OFES资料，分析了北太平洋潜流（NEUC、MUC和LUC）、南太平洋潜流（GBRUC和EAUC）和南印度洋潜流（AUC）的时间和空间分布特征，并基于温跃层以下转向的地转判据分析了其形成机制。主要结果如下：（1）在菲律宾以东海域，表层的NEC在12N附近的西边界分叉，形成向北的KC和向南的MC。在400-800米左右棉兰老岛东侧128E-130E处出现与上层海流方向相反的潜流MUC，MUC在9N和12N附近转向东并分成2支，汇入NEC下方的2支并行向东流的NEUC。到了1000米左右，吕宋岛东侧122E-124E处出现LUC，而MUC也有向岸的趋势，限制在127E以西的范围，两者在12Ｎ附近相遇，然后转向东汇入NEUC。随着深度的加深，NEUC的北侧分支流轴向北偏移。从SODA资料和OFES资料在8N、18N和138E断面的气候态年平均和月平均温度剖面可以很清晰的看出，温跃层分别呈现东高西低、西高东低和南高北低的趋势，这与各个断面上表层流和次表层逆流之间等值线倾斜方向一致。从月平均的速度剖面可以看出，MC一般位于600db以上，600db以下出现北向次表层潜流MUC，MUC春夏较强，秋冬较弱；KC一般位于500db以上，个别月份深入到2000db，其下方均有南向的LUC出现，LUC春夏较弱，秋冬较强；上层西向NEC的主体一般位于400db以上，其下方均有东向的NEUC出现，NEUC春夏较强，秋冬较弱。在北太平洋菲律宾以东海域，同时满足两个判据的区域与潜流的发生区域符合情况较好，唯一的不同在于LUC汇入NEUC的区域没有同时满足两个判据。这是由于在吕宋岛和棉兰老岛东侧，海底地形较为陡峭，海流情况较为清晰，沿岸涡较少，而且在此区域内温跃层较浅，这些都为形成温跃层以下的地转流反向提供了充分的条件。（2）在澳大利亚以东海域，表层的南赤道流（SEC）在澳大利亚东岸15S附近分叉，分为向北的北昆士兰海流（NQC）和向南的东澳大利亚海流（EAC）。500m-1000m，23S附近出现一支北向的次表层海流，沿着澳大利亚陆坡经过大堡礁抵达巴布亚新几内亚沿岸转向东，汇入新几内亚沿岸潜流（NGCUC），这支海流就是大堡礁潜流（GBRUC）。1000m-2000m，SEC下方15S附近出现东向的逆流。在2000m以下，由于地形的影响，海流局限在几个不连续的部分，而且流型较乱。从SODA资料和OFES资料在18S和30S断面的气候态年平均和月平均温度剖面可以很清晰的看出，温跃层均呈现西高东低的趋势。在18S，南向的EAC一般位于400db以上，其下方均有持续的GBRUC出现，一般有两个中心，春夏季较强，秋冬季较弱。在30S断面，EAC一般存在于2000db以上，其下方的次表层流并不规则。从此海域的气候态月平均分布来看，在大多月份没有北向的逆流存在，这说明其下方的次表层逆流并不是一个常年存在的现象。在南太平洋，同时满足两个判据的区域包括SEC下方逆流的发生区域和澳大利亚东岸的沿岸区域，这些区域部分与潜流的发生区域符合较好，只是在30S左右并没有发生潜流的区域也同时满足判据。这是由于在30S附近，温跃层较深，导致了地转流较深，同时此区域内海底地形变化比较大，虽然在此位置形成了逆向的地转流，但是因为地形的限制，在此区域内不能形成有体系的逆流。（3）在西南印度洋，SEC在非洲东岸分叉，形成一支源于25S的西南向海流——AC，这支海流平均流速达90cm/s左右，最大速度超过140cm/s。在其下方2000m左右，从35S开始在岸边出现东北向逆流——AUC，速度较小，仅为2cm/s左右。从31S、33S和35S断面的气候态年平均温度断面可以很清晰的看出，温跃层明显呈现西高东低的趋势。从月平均经向流速断面可以看出，在各个月份AC下方均出现不同强度的AUC，AC和AUC之间的等值线倾斜方向与温跃层的倾斜方向一致。在南印度洋，满足判据的区域包括南非沿岸AUC的发生区域和南非东南的部分海域，南非沿岸的AUC紧靠岸边且深度较深，这是因为此区域内温跃层较深，导致形成的地转流位置较深，而形成的逆流由于与海底的摩擦而大大削弱。南非东南部分海域满足判据，大概是由于此区域海流比较复杂，而且此海域多涡。表面风应力的强迫以及风生环流的斜压调整，使得潜流所在海域的海平面高度和温跃层倾斜方向相反，热带流涡和副热带流涡西向强化加强了该海域温跃层的倾斜程度，从而导致了次表层地转流反向。因此，大洋中次表层潜流是大洋斜压风生环流不可缺少的重要部分。但是在不同的海域存在不同的地形分布和海流分布，所以此理论只在某些合适的区域得到很好的体现。
其他摘要	Ocean circulation is the permanent flow on the basin-scale, at the same time, it is an important path of mass and heat transport and it affects the climate change deeply. The horizontal structure about the wind-driven circulation in the ocean upper layer has been known clearly, but the vertical structure was shown complicated in the recent several decades’ researches. In many regions, there exist　subsurface countercurrents under the surface currents, especially in the region near the western boundary, such as the North Equatorial Undercurrent(NEUC) under the North Equatorial Current(NEC), the Mindanao Undercurrent(MUC) under the Mindanao Current(MC), the Luzon undercurrent(LUC) under the Kuroshio(KC), the Great Barrier Reef Undercurrent(GBRUC) and the East Australian Undercurrent(EAUC) under the East Australian Current(EAC), the Agulhas Undercurrent(AUC) under the Agulhas Current(AC) et al. Now, there are less knowledge about the undercurrents than the surface currents, so it is significative to study the distributings and the dynamic mechanisms of the undercurrents by using new assimilation data and observation data, and applying the theory analyze and numerical model. In this article, the vertical and horizontal structures of the undercurrents in the north Pacific (NEUC, MUC and LUC), the south Pacific (GBRUC, EAUC) and the south Indian Ocean(AUC) were analyzed using the ARGO data, the SODA data and the OFES data. At the same time, the distributions of the criterions in apiece sea areas are analyzed. The main results are shown in the following: (1) In the region east of Philippines, surface NEC bifurcates into northward KC and southward MC at about 12N. From 400 to 800m, there exists the MUC at 128E-130E along the Mindanao coast. The MUC turns east at 9N and 12N, dividing into two branches and joining the two parallel NEUC. At about 1000m, there exists the LUC at 122E-124E along the Luzon coast, simultaneously the MUC shifts shoreward and is restricted in the area west of 127E. The MUC and LUC converge at about 12N, and turn east to join the north branch of the NEUC which shifts northward in the deeper layer. The distributions of temperature along 8N, 18N, and 138E sections show that the thermocline slope down westward, eastward and northward respectively. The southward MC locates upon 600db and there exists northward MUC below 600db. The northward KC locates upon 500db and there exists southward LUC below 400db. The NEC locates upon 400db and there exists eastward NEUC below it. The MUC and the NEUC is stronger in spring and summer than autumn and winter, contrarily the LUC is stronger in autumn and winter than spring and summer. In the region east of Philippines, the areas where the two criterions are met roughly overlap the areas of undercurrents, and the only difference is that the area near the LUC is not connected with the area near the NEUC. The reason may be that the topographty east of Luzon and Mindanao is abrupt, there are few eddies along the coast and the distributing of currents is clear, at the same time, thermocline in this region is shallow, so there are permanent undercurrents in this area. (2) In the region east of Australia, SEC bifurcates into northward North Queesland Current (NQC) and southward East Australia Current (EAC). From 500m to 1000m, there exists a northward subsurface current, and flow along the coast of Australia. The subsurface undercurrent- GBRUC turns east after arriving PNG and join into the NGCUC. From 1000m to 2000m, there exits a countercurrent under SEC. Below 2000m, the currents locate at several discrete regions because of the topograph, and these currents are unregular. The distributions of temperature along 18S and 30S sections show that both thermocline slope down eastward. In the 18S section, the southward EAC locates upon 400db, and there exist GBRUC with two cores. The GBRUC is stronger in spring and summer than autumn and winter. In the 30S section, the EAC locates upon 2000db, but the subsurface currents are unregular. From monthly distributings in this region, there aren’t undercurrents in a majority of months, that is to say, the EAUC are not a permanent phenomenon. In the region east of South Africa, the areas where the two criterions are met include the area where exists the undercurrents under SEC and the area along the east coast of Australia. These areas roughly overlap the areas of undercurrents, the only difference is near 30S. That is because that thermocline near 30S is deep, so the position of the geostrophic currents is deep, at the same time the topograph in this area is flat. All these result in that there is not a system of undercurrents because of the limits of the topograph. (3) In the southwest Indian Ocean, SEC bifurcates at east coast of Africa and builds the southwestward AUC, and the average velocity of this current is larger than 140cm/s. At about 2000m, there exists a countercurrent-AUC from 35S, and the velocity is smaller than 2cm/s. The distributions of temperature along 31S, 33S and 35S sections show that all thermocline slope down eastward. In the sections of monthly meridional velocity, there exists AUC in each month and the slope of the isoline between the AUC and AC is apparently similar to that of thermocline. In the Indian Ocean, the areas where the two criterions are met include the area along the east coast of South Africa, and the part area east of South Africa. The depth of AUC is very deep, and it clings to the coast closely. That is because thermolcine in the area is deep, so the position of geostrophic currents is deep, and the intensity of geostophic currents is weaken for the friction in the seabed. There are many eddies in the region east of South Africa, so this area meets the criterions. The force of the surface wind curl and the baroclinic adjustment of the wind-driven circulation lead to the inversed slope of SSH and thermocline in the countercurrents areas. According to the westward intensification, the slope of thermocline along the western boundary was significantly strengthened, resulting in geostrophic velocity inversion. So it can be considered that the subsurface countercurrents in the oceans should be the inevitable part of baroclinic wind-driven circulation. Because of the distributing of topographty and currents in different area, this theory only can be used in certain area.
页数	109
语种	中文
文献类型	学位论文
条目标识符	http://ir.qdio.ac.cn/handle/337002/1221
专题	海洋环流与波动重点实验室
推荐引用方式 GB/T 7714	臧楠. 若干大洋西边界潜流的分布特征及其形成机制[D]. 海洋研究所. 中国科学院海洋研究所,2008.

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