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题名: 台湾东北黑潮入侵的季节和年际变化特征及影响因子分析
作者: 曹蕾
学位类别: 博士
答辩日期: 2016-05
授予单位: 中国科学院大学
授予地点: 北京
导师: 侯一筠
关键词: 黑潮入侵 ; 台湾东北 ; 季节变化 ; 年际变化 ; 影响因子
学位专业: 理学博士 物理海洋学
中文摘要: 黑潮流经台湾东北海域时部分黑潮水向东海陆架入侵不仅对陆架及沿岸海域的温盐状况、环流结构产生影响,而且其所带来的营养物质对近海生态环境产生重要影响。本文在前人研究工作的基础上,以黑潮在台湾东北海域向岸入侵为研究对象,分析入侵的季节变化和年际变化特征、规律,并分析其变化的影响因子。之后,结合ROMS数值模式设计并实施敏感性实验以验证和区分不同影响因子对入侵的作用,最终初步给出不同影响因子对入侵的季节和年际变化的贡献,主要得到以下结论:
利用WOCE-SVP项目的漂流浮标资料反演表层流场的季节特征,以及利用HYCOM再分析资料得到跨200 m等深线整层向岸体积输送的季节特征,发现冬季主要入侵路径很贴近台湾岛北端,夏季表层不存在紧贴台湾岛岸线的入侵现象。对1993~2014年AVISO提供的台湾东北海域海表面地转流速异常场的年际变化时间序列进行经验正交函数(EOF)分解,得到年际尺度上的主要模态。第一模态是由黑潮流轴的东西摆动与(靠近台湾岛北端)跨陆坡异常分支组成的气旋/反气旋式环流结构。第二模态的异常流动贯通式地跨越200 m等深线表达了黑潮流轴的南北摆动。
季节尺度上,冬季上游(黑潮进入东海入口处)黑潮流向向北偏转程度大,流轴向岸偏移,对应入侵增强;夏季则相反。风应力强迫可能是影响晚秋和初冬入侵的因素之一。海表面冷却可能是冬季黑潮向台湾东北陆架入侵的影响因子。台湾海峡流动可能对入侵的季节变化有影响。
年际尺度上,第一模态入侵的年际变化与上游流量呈负相关,与上游流动的流向呈正相关,与纬向风年际变化呈负相关,与海表面热通量呈负相关。当台湾以东水道黑潮流量减弱、流向偏北时,利于入侵。当台湾东北海域西风加强时,入侵增强。台湾东北冷却加强对应第一模态形式的入侵加强。影响第二模态的并非上游流量,而是台湾以东水道122.3ºE~122.8ºE范围的流动异常。第二模态与经向风年际变化和台湾海峡体积输送的年际变化呈负相关。ENSO、PDO等大洋因子可能通过台湾以东海域的中尺度涡为媒介来达到影响黑潮以第一模态入侵东海的目的。台湾岛东侧122.5ºE~124ºE,22.5ºN~24ºN海域的涡度年际异常是引起台湾东北黑潮以第一模态形式向岸入侵异常的重要因素之一。
在敏感性实验中,对于122.8ºE以西跨200 m等深线的向岸体积输送,台湾海峡流动对其的加强作用在秋冬季节最为显著,上游流量的加强作用在冬春季节最为显著,风应力在夏季和冬季的加强作用显著,对冬季而言,海表面热通量的加强作用主要体现在2~3月。上游流动和台湾海峡流动情况是影响黑潮在台湾东北向岸入侵年际变化的主要因子。风应力的强迫作用主要体现在风场进行年代际转换的时间1996~2001年,其余年份不显著。海表面热通量引起的年际变化不显著。
英文摘要: Kuroshio onshore intrusion (KOI) northeast of Taiwan has an important impact on the circulation structure in East China Sea and coastal ecosystems of China. In this article, we aim at investigate characteristics of KOI northeast of Taiwan and impact factors of its seasonal and interannual variations. Besides, we design and implement a series of sensitivity experiments using ROMS model to explore the role of different impact factors. The finding and conclusions are as follows.
Firstly, seasonal characteristics of surface flow are obtained by using WOCE-SVP project drifting buoy data, and features of the Kuroshio onshore volume transport across the 200 m isobaths are obtained by using HYCOM reanalysis data. The main route of KOI is very close to the northern coast of Taiwan island in winter, while the KOI is not happened at surface in summer. The significant spatial patterns and their temporal variations of interannual characteristics are obtained from empirical orthogonal function (EOF) analysis on surface geostrophic velocity anomaly from 1993 to 2014 provided by AVISO. The first EOF mode (EOF1) illustrates a east-west shift of Kuroshio axis and a KOI anomaly pattern in the form of anticyclonic/cyclonic circulation anomaly structure. The second mode (EOF2) shows a throughflow anomaly pattern across the 200 m isobaths and the north-south shift of Kuroshio axis.
The impact factors of the multi-temporal-scale variations of KOI are analyzed. The flow direction of upstream Kuroshio truns anticlockwise (clockwise) relative to the climate mode in winter (summer), and the Kuroshio’s axis makes an onshore (offshore) shift, which corresponding to the enhanced (weakened) intrusion. Wind stress forcing maybe make an effect on the intrusion in the late autumn and early winter. Surface heat flux may influence the KOI northeast off Taiwan by cooling in winter. Seasonal changes of the flow through the Taiwan Strait forcing by large-scale wind may have an impact on the KOI.
On the interannual scale, the time coefficient of EOF1 shows negative correlations with the upstream flow, zonal wind and sea surface heat flux, while is positively correlated with the direction of upstream flow. A weakened upstream Kuroshio and a relatively anticlockwise shift of flow direction promote the surface onshore intrusion. Strengthened westerly wind and cooling northeast of Taiwan is corresponding to the strengthened intrusion. For the first mode, ENSO, PDO and other oceanic factors may influence the intrusion through a medium such as eddies arrived at east off Taiwan (122.5ºE~124ºE, 22.5ºN~24ºN). The time coefficient of EOF2 shows a correlation with the anomaly flow in the range of 122.3ºE ~ 122.8ºE east of Taiwan, and a negative correlation with the interannual variability of the meridional wind and the volume transport through Taiwan Strait.
Finally, a series of sensitivity experiments are implemented to compare the contribution of different factors on the KOI northeast of Taiwan. For the volumn transport across the 200 m isobaths west of 122.8ºE, the flow through Taiwan Strait is the most important factors, which strengthen the intrusion in autumn and winter. The upstream Kuroshio can cause obvious onshore intrusion in winter and spring. Wind stress strengthens the intrusion in late autumn and early winter. In winter, the cooling enhances intrusion in February and March. For the interannual variability of the surface and vertical-integrated onshore intrusion, upstream Kuroshio and the flow through Taiwan Strait are the main factors. Wind stress effects the intrusion in the period of the decadal conversion from 1996 to 2001, and has no obvious effect in the rest time. Surface heat flux forcing is not an important impact factor.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.qdio.ac.cn/handle/337002/116976
Appears in Collections:海洋环流与波动重点实验室_学位论文

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作者单位: 中科院海洋研究所

Recommended Citation:
曹蕾. 台湾东北黑潮入侵的季节和年际变化特征及影响因子分析[D]. 北京. 中国科学院大学. 2016.
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