IOCAS-IR  > 海洋环流与波动重点实验室
太平洋赤道潜流的水团来源及其输运路径
聂珣炜
学位类型博士
导师王凡
2017-05-27
学位授予单位中国科学院大学
学位授予地点北京
学位专业物理海洋学
关键词赤道潜流 水团 输运通道 北太平洋热带水 潜沉
摘要
太平洋赤道潜流(EUC)是存在于赤道太平洋次表层中的一条强劲的东向洋流,它不仅构成了太平洋赤道海域中温跃层的主体,同时还是冷舌区上升流的主要水源。因此无论在表层还是次表层,赤道太平洋海水的温盐特性都受到EUC显著影响。此外,EUC还是太平洋中若干经向翻转环流圈(MOC)共同的位于赤道上的重要分支。这些MOC包括位于赤道两侧的副热带环流圈(STCs)、热带环流圈(TCs)以及连接太平洋与印度洋的跨洋环流(IOC)。其中,TCs能够将热带表层水带入EUC中;STCs和IOC能够将形成于中高纬度海域的水团带入热带海域,并使这些水团最终在EUC中汇聚在一起。因此研究EUC的水源构成以及它们向赤道的输运路径,可以帮我们进一步了解太平洋热带海域与热带外海域之间的相互作用,具有重要的研究意义。
本文使用ECCO模式资料,结合伴随浓度示踪物追踪法,对EUC的水团来源、输运时间、输运通道等问题进行了详细的分析和讨论。结果表明,位于中太平洋的EUC中近70%的水体源自纬度较低的热带海域及副热带东部海区。其中,源自副热带东部海区的水团对EUC的贡献约为50%,而且来自南太平洋副热带东部水团的贡献是北太平洋的3倍多。关于EUC水源输运时间的研究结果表明,热带外水源中约有60%的水体从其潜沉区向赤道输运所需时间小于20年,而且这部分水源主要是来自副热带东部海区的水团;绝大部分热带水体的输运时间小于1年。虽然EUC的主体部分始终是由热带外水体构成的,但是从西太平洋到东太平洋EUC中的热带水体和热带外水体所占比重发生了明显变化。在西太平洋,EUC中的热带外水体所占比重略高于中东部海域;从西太到中太,这一比重缓慢下降;从中太到东太,两部分水体之比基本保持稳定,热带外水体约为热带水体的4倍。西边界通道和内区通道对EUC的贡献同样沿着赤道由西向东发生了显著的变化。总体来说,西边界通道在西部海区占主导;内区通道在东部海区占主导。在热带外水体向EUC的输运过程中,西边界通道与内区通道的贡献之比由西向东逐渐减小,但西边界通道始终占主导。热带水体则主要通过内区通道向赤道进行输运。至少有60%的热带水体通过TCs汇入EUC中,而非在局地通过垂向混合或者混合层起伏等过程汇入EUC。而且热带水体更加趋向于通过赤道北部的TC汇入EUC。在从源地向赤道的输运过程中,EUC中水体受到混合作用的显著影响,水体特性发生了明显的改变,而且热带内的混合强度不亚于热带外。
北太平洋热带水(NPTW)是EUC位于北太平洋的主要水源之一。通过前面的研究内容可知,NPTW的重要性不仅体现在它对EUC的贡献量较大,同时还体现在它向赤道的输运时间明显短于其它热带外水源。因此为了进一步了解北太平洋副热带海域与热带海域之间相互作用过程,本文对NPTW进行了重点研究。采用浓度示踪物追踪法,我们对该水团的潜沉以及向赤道的输运过程进行了系统的追踪实验和分析讨论。结果表明,NPTW形成于北太平洋副热带海域的海表盐度极大值区,但其主要潜沉区则集中于该区域的东部海域。潜沉之后,NPTW的主体部分首先跟随北赤道流(NEC)流向西部,并在到达西边界后分为两个部分:一部分跟随黑潮流向北部,另一部分则通过西边界通道或者内区通道向太平洋热带海域输运。值得注意的是,在向赤道输运的过程中,通过西边界通道向赤道输送的NPTW中只有一少半能够最终汇入EUC并随之到达赤道太平洋的中东部海域,原因是印尼贯穿流(ITF)具有明显的分流作用,很大一部分NPTW的水通过ITF进入印度洋海域而不是EUC。在ITF的影响下,内区通道的贡献变得不可小觑,在最终到达赤道太平洋海域的NPTW中,有大约30%是来自内区通道,与西边界通道同等量级。但是与南太平洋热带水(SPTW)向赤道的输运过程相比(西边界通道与内区通道的输送量相当),北太平洋中内区通道的贡献仍然是偏弱的。同样是受到ITF分流作用的影响,导致最终能够在赤道太平洋中东部海域的上翻至混合层的NPTW只占总量的18%,这一比例要远低于SPTW(30%)。上述结果详细阐述了EUC的主要水源之一——NPTW的潜沉及其输运过程,揭示了ITF在NPTW向赤道的输运过程中所扮演的重要角色,并明确了其与SPTW对EUC贡献的差异,为进一步研究热带外水团对热带海域的影响以及EUC对热带海域的海洋环流过程及气候效应影响奠定了基础。
 
其他摘要Equatorial Undercurrent (EUC) is a strong eastward current that exit in the subsurface of the tropical Pacific. It constituts the main part of the thermocline alone the equator and it is also the main water source for the upwelling in cold tounge region. Therefore, EUC play an important role in modulating the variation in equatorial Pacific, no matter in the surface or the subsurface. Besides, EUC is the main branch of several meridional overturning circulations on the equator. These meridional overturning circulations include the Subtropical Cells (STCs) and Tropical Cells (TCs) in each hemisphere and the interocean circulation (IOC) connecting the Pacific and Indian ocean. Water masses that formed in high and mid-latitude regions could be transported into the tropical region by STCs and IOC, and eventually converge within the EUC. So it is of great significance to have a comprehensive understanding of the water sources of the EUC and their equatorward pathways which can help us to learn more about the interaction between the tropical region and extratropical region in Pacific.
An adjoint passive tracer of the consortium Estimating the Circulation and Climate of the Ocean (ECCO) is used to determine the water sources of the Pacific Ocean Equatorial Undercurrent (EUC) in a global circulation model. The primary water sources of the EUC are identified, as well as the transit time and pathways of these water sources. The results shows that, 70% of the EUC in central Pacific is constitute of water sources that originated from low latitude regions, including tropical region and eastern subtropical regions in both hemispheres. Particularly, water masses originated fromt eastern subtropical region contribute 50% of the EUC transport, and the amount of water from the south is more than 3 times larger than that from the north. The majority of tropical water has a transit time less than 1 year. 60% of the extratropical water has a transit time less than 20 years, among which most is originated from eastern subtropical regions. Although the main part of the EUC is constitude by extratropical water, the percent of tropical water and extratropical water within the EUC changes slightly from west to east. In western Pacific, the percent of extratropical water is relatively high; from western Pacific to central Pacific, the percent of extratropical water slightly reduced; from central Pacific to eastern Pacific, the percent of extratropical water and tropical water in the EUC remain basically the same. The contribution of the western boundary pathways and the interior pathways to the EUC changes from west to east as well. In general, the western boundary pathways is dominate in the western part of the EUC, while the interior pathways is dominate in the eastern part of the EUC. In the transportation of extratropical water from the formation region to the EUC, western boundary pathways are more important than the interior pathways, while the relative importance is more significant in the western Pacific. The tropical water is converged into the EUC mainly through the interior pathways. As shown by the results, at least 60% of the tropical water is transported via the TCs instead of local vertical processes. And the tropical water transport via the TC in north side of the equator is more than that in the south. At last, the distribution of EUC water sources against density, temperature and salinity in different period shows that the mixing effect within the tropical region is no weak than that in the extratropical region.
To enhance the understanding of the interaction between the North Pacific Subtropical region and the tropical region, one water source of the EUC that originated from the subtropical North Pacific are investigated in this study. NPTW is one of the water sources of the EUC that originated from the eastern subtropical region in North Pacific, and it is characterized as a subsurface salinity maximum. The subduction and equatorward pathways of NPTW are investigated using a simulated passive tracer of ECCO. The results demonstrate that the the main subduction region of NPTW lies in the eastern part of the sea surface salinity maximum region. After subduction, the main body of NPTW first spreads westward in the North Equatorial Current. Then it splits into two branches. One flows northward in the Kuroshio upon reaching the western boundary, and the other enters the tropical Pacific either via its western boundary pathway (WBP) or interior pathway (IP). Less than half of the transport through the western boundary pathway can eventually reach the central and eastern Pacific by the Equatorial Undercurrent, while the rest is seen to flow into the Indian Ocean by the Indonesian Throughflow. As a result, the interior pathway is found to play a significant role in equatorward transport of the NPTW. About 30% of the NPTW that reached the equatorial Pacific is transported through the interior pathway. However, the percent of NPTW that transport through the interior pathway is still weaker than its counterpart, the South Pacific Tropical Water (SPTW). Also due to the bypass of the ITF, the percent of NPTW (18%) that could finally upwell into the mixed layer of central and eastern tropical Pacific is also less than the SPTW (30%). These result clearly show the subduction and transport of the NPTW, clarify the strong influence of ITF on equatorward transport of the NPTW and the differences between the NPTW and SPTW, and lay a foundation for further studies about the influence of NPTW and SPTW to the equatorial region.
学科领域物理海洋学
文献类型学位论文
条目标识符http://ir.qdio.ac.cn/handle/337002/136627
专题海洋环流与波动重点实验室
作者单位中国科学院海洋研究所
推荐引用方式
GB/T 7714
聂珣炜. 太平洋赤道潜流的水团来源及其输运路径[D]. 北京. 中国科学院大学,2017.
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