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北太平洋副热带模态水潜沉率变异规律及其机制研究
王然
Subtype博士
Thesis Advisor于非
2016-05-18
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Discipline理学博士 物理海洋学
Keyword副热带模态水 潜沉率 混合层深度 变异趋势
Other Abstract        北太平洋副热带模态水是冬末海气相互作用产生的垂向性质均一的低位涡水,可以将气候变 化的异常信号通过潜沉的作用进入永久性密度跃层,并且向低纬度海域输运,对低纬度海域的气候异常有重要影响。因此,认识和了解北太平洋副热带模态水潜沉的变异规律和变异机制,有助于进一步掌握北太平洋副热带和热带之间的相互作用,是海洋与大气相互作用研究的热点问题之一。
       目前对于潜沉率的研究大多是依赖于对模式数据的分析,利用观测数据对潜沉率年际、年代际变异和变异机制的研究较为稀少,然而,Argo数据从2001年持续至今,随着Argo观测网络的日渐完善,已经可以提供十年以上的有效数据支持大尺度海洋过程的研究。本文利用2003-2013年逐月Argo观测数据和1960-2010年SODA数据,对北太平洋副热带西部模态水(the Subtropical Mode Water, STMW),东部模态水(the Eastern Subtropical Mode Water,ESTMW),以及中部模态水(the Central Mode Water,CMW)潜沉率的变异规律和变异机制进行了系统的分析,并且得到了一些创新性的研究成果。
       首先,根据北太平洋副热带模态水STMW、ESTMW和CMW的潜沉区进行划分,选择28°-35°N,140°E-180°作为STMW的潜沉区,36°-45°N,145°E-160°W为CMW潜沉区,20°-28°N,150°W-120°W为ESTMW潜沉区。潜沉区的潜沉率平均时间序列以及EOF分析的空间分布都显示,STMW、ESTMW和CMW的潜沉率异常主要是来自侧向输运项异常的贡献,体现了混合层深度异常对潜沉率异常的作用。
       通过控制晚冬温度和盐度的气候态或者逐年的变化,北太平洋模态水潜沉区内的晚冬混合层深度进行控制变量分析显示,在STMW和ESTMW潜沉区内,晚冬混合层温度异常是混合层深度异常的主要因素,盐度异常并不会带来混合层深度的显著变化,而在CMW潜沉区内,晚冬混合层盐度异常表现出了和温度异常相当的作用。
       副热带模态水潜沉区的晚冬热收支及CMW潜沉区的晚冬盐度收支分析结果中,STMW和CMW潜沉区内,晚冬混合层热收支变异与平流项变异和热通量项都存在显著正相关的关系,Argo数据显示在2003-2013年间,热收支的增强趋势主要收到了来自平流项增强趋势的贡献。ESTMW潜沉区内,夹卷项与热收支相关性显著,并且2003-2013年间只有夹卷项与热收支项都存在减弱的趋势。盐度收支的结果也体现了平流作用在CMW潜沉区的重要作用。
SODA数据结果在模态水潜沉率年际变异规律和变异机制上都表现出了与Argo数据结果的一致性,结合1960-2009年SODA和2003-2013年Argo潜沉率结果进行年代际变异规律进行研究,1970s气候突变前后,STMW、ESTMW和CMW潜沉率都存在明显的突变,而随着1980s后一段时间PDO指数变异趋势的减弱,模态水潜沉率也保持着平缓的变化,直到2000年后PDO位相发生转变,STMW和CMW产生了较强的减弱趋势,而ESTMW也表现出了加强的趋势,因此,2000年后可能存在气候突变的新节点,并且副热带模态水潜沉率的变异也开始响应了这一突变。;         The North Pacific subtropical mode waters are formed in late winter due to ocean-atmosphere interaction. Climate change signal can be sent in to the permanent pycnocline through subduction of these mode waters, and then transferred to the tropical area. It is significant to study the features and mechanism of the variations of subtropical subduction, since it would help further study the exchange between subtropical and tropical oceans. And subduction is one of the issues of great interests among the researches of ocean-atmosphere interaction.
          Most of past researches of subtropical subduction variations were completed with numerical model data, but few are studied with observational data. However, Argo system has continued until now since 2001, and valid data since 2003 is available for large scale ocean researches as the Argo floats deployed more and more concentrated. In this work, variability and variation mechanism of subduction of the North Pacific subtropical mode waters, including the western subtropical mode water (STMW), the eastern subtropical mode water (ESTMW), and the central mode water (CMW), are analyzed with monthly mean Argo data from 2003 to 2013 and SODA data from 1960 to 2010. The major results are as follows.
          Firstly, according to the climate mean distribution of North Pacific subtropical subduction, choose 28°-35°N, 140°E-180° as the STMW subduction region, 20°-28°N, 150°W-120°W as the ESTMW subduction region, and 36°-45°N, 145°E-160°W as the CMW subduction region. The spatial and temporal distribution both showed that lateral induction term anomalies, corresponding to the horizontal gradient of mixed layer depth, have played the most important roles in subduction rate anomalies of STMW, ESTMW and CMW. It presented that, in North Pacific, late winter mixed layer variation is important in controlling the subduction rate variation.
        Diagnostic analysis of mixed layer variation was made by controlling either the annual variation or climate mean of temperature and salinity. The results showed that late winter mixed layer depth variation was mainly due to the mixed layer temperature variation in STMW and ESTMW subduction region. In the CMW subduction region, late winter mixed layer temperature and salinity changing both contribute to the mixed layer variation.
          Heat storage analysis was made of the later winter North Pacific mixed layer. In the STMW and CMW subduction region, heat storage advection term variations corresponds well with the heat storage tendency, and trend of the advection term also contributed most to the positive trend of the heat storage tendency during 2003-2013 according to Argo data. In the ESTMW subduction region, it is the entrainment term correlating with heat storage tendency significantly. According to the Argo data analysis, it is also the trend of entrainment term contributed to the negative trend of heat storage in the ESTMW subduction region during 2003-2013. Salinity budget analysis was also made of the late winter mixed layer salinity in the CMW subduction region. The result presented that horizontal advection effect also play an important role in the late winter mixed layer salinity variation in the CMW region.
        Since the results of variability and variation mechanism analysis of SODA and Argo correspond well with each other, we combined the SODA result during 1960-2009 with the Argo result during 2003-2013 to discuss decadal variation of North Pacific subduction rate. Around the abrupt climate change in late 1970s, all of the subduction rates of STMW, ESTMW and CMW showed a strong trend. Later the North Pacific subduction rates have showed weak trends for a long time, as the PDO index varied gently since 1980s. According to the Argo data analysis, subduction rates of STMW and CMW presented strong weakening trends during 2003-2013, and subduction rate of ESTMW presented enhanced strengthening trend during 2003-2013. Abrupt climate change might have happened after 2000, as a PDO phase transition was found, and the North Pacific subduction rates have responded well with this change.
Subject Area海洋物理学
Language中文
Document Type学位论文
Identifierhttp://ir.qdio.ac.cn/handle/337002/112531
Collection海洋环流与波动重点实验室
Affiliation1.中科院海洋所
2.中国科学院大学
Recommended Citation
GB/T 7714
王然. 北太平洋副热带模态水潜沉率变异规律及其机制研究[D]. 北京. 中国科学院大学,2016.
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