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庆良间水道水交换及其对东海黑潮的影响
周文正
学位类型博士
导师于非
2017-03-30
学位授予单位中国科学院大学
学位授予地点北京
学位专业环境工程
关键词庆良间水道 黑潮 琉球流 中尺度涡 水团
摘要庆良间水道位于琉球岛链的冲绳岛和宫古岛之间,水道的宽度仅为50Km,但是海槛深度可以达到1050m,是宫古海峡乃至整个琉球岛链上最深的通道,庆良间水道对东海和西太平洋的水交换起到了重要的作用。虽然庆良间水道的平均流量很小,但是流量的变化很大,水道剧烈的流量变化对其上下游东海黑潮的变异产生了重要的影响。由于庆良间水道地区的实测资料非常的匮乏,本文利用网上公开的观测资料结合模式数据研究了庆良间水道的水交换特征,分析了庆良间水道水交换对其上下游东海黑潮的流量和水团特性的影响,最后讨论了中尺度涡、黑潮以及琉球流对水道水交换的影响及机制。研究的主要结果有以下几点:
(1)庆良间水道的平均流量约为1.93Sv,但是流量可以从-9.9Sv变化到13.9Sv,变化的标准差可以达到4.3Sv。太平洋的水通过庆良间水道流入东海主要发生在水道的次表层(300-500m),并且次表层的入侵可能与庆良间水道东部的琉球流有关。庆良间水道的流量变化表现出显著的季节变化特征,其中春季流量最强,秋季次之,冬季较弱,夏季最弱。庆良间水道流量的年际变化在春季和冬季都有增加的趋势,在夏季和秋季都有减弱的趋势,其中春季的增加趋势最为显著,秋季的减弱趋势最为显著。
(2)庆良间水道上游黑潮断面之间的流量变化表现出很强的空间一致性,但是庆良间水道上下游之间的黑潮流量变化却表现出显著的差异,这一差异主要是由庆良间水道的水交换和陆架水的输入共同导致,但是庆良间水道的贡献起到了主要作用。庆良间水道的流量变化与其下游黑潮PN断面的流量变化表现出比较强的正相关关系。
(3)西太平洋通过庆良间水道入侵东海黑潮导致下游黑潮次表层高盐水的盐度增加,深度变浅,同时也导致下游黑潮中层低盐水的盐度减小,深度加深。黑潮上下游次表层高盐水和中层低盐水盐度的季节变化不一致,次表层高盐水的盐度变化可能受到了表层淡水通量,庆良间水道流量和上游黑潮PM断面流量的季节变化影响,在冬季最强,秋季次之,春季较弱,夏季最弱,然而中层低盐水盐度的季节变化主要受庆良间水道流量和上游黑潮PM断面流量变化的影响在秋季最强,春季次之,冬季较弱,夏季最弱。
(4)庆良间水道的流量变化由其两侧的海表面高度差决定,而两侧海表面高度的变化主要受西传的中尺度涡影响。中尺度涡对于庆良间水道流量变化的影响主要由涡的六种位置决定,当反气旋涡(气)位于庆良间水道东北部或者气(反气)旋涡位于庆良间水道的西南部,庆良间水道的流量表现为正(负)异常;然而当气旋涡或者反气旋涡位于庆良间水道的中间位置时,庆良间水道的流量变化相对较弱。 中尺度涡对庆良间水道流量变化的影响机制可以用水团平衡和正压绕岛理论解释。前者揭示庆良间水道两侧的辐聚辐散导致海表面高度差发生变化,从而导致庆良间水道的流量发生变化。后者揭示中尺度涡与冲绳岛和宫古岛摩擦产生的能量耗散引起了绕岛的涡流,涡流导致庆良间水道的流量发生变化。
(5)东海黑潮和琉球流对庆良间水道的流量变化也产生了重要的影响。黑潮对庆良间水道水交换的影响主要由水道上游黑潮流量的大小以及主轴的摆动决定。当水道上游黑潮的流量增加(减小),或者主轴的位置离庆良间水道越近(越远)时,将会有更多(更少)的水从东海通过庆良间水道流入太平洋,从而导致庆良间水道的流量减小(增加),最终导致黑潮PN断面的流量减小(增加)。琉球流对庆良间水道流量变化的影响主要体现在水道东北部和西南部琉球流的流量差,流量差的变化与庆良间水道的流量变化表现为显著的正相关关系。此外,当水道西南部琉球流的流量增加(减小)时,将会导致庆良间水道的流量减小(增大),然而当水道东北部琉球流的流量增加(减小)时,将会导致庆良间水道的流量也增加(减弱)。
其他摘要The Kerama Gap, located between the Okinawa Islands and Miyakojima Island (~50Km), is the deepest channel in the Miyako strait and the Ryukyu Island chain with a sill depth of 1050 m, which plays an important role in the water exchange between the East China Sea (ECS) and Northwestern Pacific (NP). Although the mean Kerama Gap transport (KGT) is small, the variation of KGT is large, resulting a significant influence on the variation between the Kuroshio upstream and the downstream. Due to the deficiency of observational data, we investigate the water exchange through the Kerama Gap by using the combination of public observation data and model. Then we analysis the effects of water exchange through the Kerama Gap on the transport variation and water properties between the Kuroshio upstream and downstream. Finally, we discuss the dynamic mechanism of the effects of mesoscale eddies, Kuroshio and Ryukyu Currents on the water exchange through the Kerama Gap. The main results and conclusions are as follows:
(1) The mean KGT is 1.93Sv from the NP into the ECS,but the monthly KGT has a large variability with a maximum of 13.9 Sv and a minimum of -9.9Sv with a standard deviation of 4.3Sv. Pacific water flow into the ECS through the Kerama Gap mainly in the subsurface layer (300-500m),which may be induced by the east Ryukyu Currents. The seasonal variability of KGT is significant, which is strongest in spring, second stronger in spring, weaker in winter and weakest in summer. The inter-annual variability of KGT has an increasing tendency in spring and winter and decreasing tendency in summer and autumn. The most significant increasing tendency is in spring and the most decreasing tendency is in autumn.
(2) Volume transport between the Kuroshio upstream transects were spatially consistent, but there was a significant discrepancy between the Kuroshio upstream transport and downstream transport; This discrepancy was contributed by the KGT and the continental shelf water, but the variation of KGT plays the most important role. The variation of KGT shows a positive correlation with the variation of Kuroshio transport across the PN line (KNT).
(3) The intrusion of NP into the ECS via the Kerama Gap has a significant influence on the water properties of the downstream Kuroshio, which increases the salinity of the Kuroshio subsurface water and decreases the salinity of Kurshio intermediate water. Besides, the subsurface water depth become much shallower and the intermediate water depth becomes much deeper. The seasonal variation of the subsurface water salinity and the intermediate water salinity between the upstream and downstream Kurshio is not consistent. The seasonal variation of subsurface water salinity may be influenced by the combination of the variation of KGT, KMT and the surface freshwater flux, which is maximum in winter, second in autumn, third in spring, and minimum in summer. However, the seasonal variation of intermediate water salinity is mainly influenced by the variation of KGT and KMT, which is maximum in autumn, second in spring, third in winter, and maximum in summer.
(4) The variation of KGT is mainly determined by the variation of sea level difference (SLD) across the Kerama Gap, and these differences are dominated by the westward propagating mesoscale eddies. The effects of mesoscale eddies on the variation of KGT depend on the meridional location of these eddies. When the anticyclonic (cyclonic) eddy is located in the northeast of the Kerama Gap or the cyclonic (anticyclonic) eddy is located in the southwest of the Kerama Gap, the KGT shows a strong positive (negative) anomaly. However, when the anticyclonic or cyclonic eddy is located in the central region of the Kerama Gap, the KGT shows a relatively smaller anomaly. The dynamic mechanism underlying the effects of mesoscale eddies on the variation of KGT may be explained by the mass balance analysis and barotropic island rule. The former indicates that the relative strength of the mass convergence to divergence makes a great contribution to the variation of KGT. The latter suggests that energy dissipation in the boundary between the eddy and the Okinawa Islands or Miyakojima Island induced the streamer flowing around the islands, which caused the variation of KGT.
(5) The ECS-Kuroshio and Ryukyu Currents also have an influence on the variation of KGT. The influence of Kuroshio is mainly determined by the KMT and the shift of Kuroshio central position (KCP). When the KMT is high (low) or the KCP shifts toward (away from) the Kerama Gap, there will be more (less) water flowing from the ECS to the NP through the Kerama Gap, resulting the decreasing (increasing) of KGT and finally the KNT. The influence of Ryukyu Currents is mainly determined by the transport variation of Ryukyu currents between the northeastern and southwestern of the Gap, which shows a positive correlation with the KGT. Besides, the increasing (decreasing) volume transport in southwest of the Gap results the decreasing (increasing) KGT. However, the increasing (decreasing) volume transport in northeast of the Gap results the increasing (decreasing) KGT.
学科领域环境工程学
语种中文
文献类型学位论文
条目标识符http://ir.qdio.ac.cn/handle/337002/136542
专题海洋环境工程技术研究发展中心
作者单位1.中国科学院大学
2.中国科学院海洋研究所
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周文正. 庆良间水道水交换及其对东海黑潮的影响[D]. 北京. 中国科学院大学,2017.
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