North Pacific Tropical Water: its climatology and temporal changes associated with the climate regime shift in the 1970s
North Pacific Tropical Water: its climatology and temporal changes associated with the climate regime shift in the 1970s
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DOI：
10.1016/s0079-6611(00)00037-9
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发表时间：
2000-10
影响因子：
4.1
通讯作者：
T. Suga;A. Kato;K. Hanawa
中科院分区：
文献类型：
--
作者：
T. Suga;A. Kato;K. Hanawa
北太平洋热带水（NPTW）的特点是北赤道流的地下盐度最大，是北太平洋盐的主要来源。本文简要描述了其形成和环流的气候学特征，并分析了其与20世纪70年代气候变化有关的时间变化特征。我们使用了多种数据，包括沿130°E、137°E、144°E和155°E子午线的重复水文剖面，夏威夷海洋时间序列的水文数据，1994年世界海洋地图集，以及现有的风应力和蒸发网格数据。证实了NPTW起源于以国际日期变更线为中心的20°-30°N海面盐度最高区，沿等平地转流模式扩散的经典观点。结果表明，沿137°E的NPTW经向范围平均为10°N ~ 23°N，盐度最高的岩心位于15°N和24.0σθ附近，北（南）约15°N的NPTW部分来自日期线以西（东）的地层区。137°E剖面的NPTW与20世纪70年代中期的气候变化密切相关。在15°N以北，NPTW的盐度和厚度都有所增加，而在15°N以南，NPTW的盐度增加，厚度保持不变。NPTW南北两侧西向地转速度均显著增加。北部的增厚加速和南部的加速增加了NPTW穿越137°E的输送。NPTW形成区蒸发和Ekman盐辐合等热盐强迫的变化可能是NPTW南部盐度升高的原因，而不是北部盐度升高的原因。另一方面，增加的Ekman泵送导致137°E的NPTW库存和运输增加。137°E NPTW盐度的增加，特别是其北部部分盐度的增加，可能是由于其形成速率的增加，而不是其形成区域海面盐度的变化；NPTW层越厚，在混合过程中幸存下来的岩心越咸。
North Pacific Tropical Water (NPTW) is characterized as a subsurface salinity maximum flowing in the North Equatorial Current and is the main source of salt for the North Pacific. We briefly describe the climatological features of its formation and circulation, and then examine temporal changes in its properties associated with the climate regime shift in the 1970s. We use a variety of data, which include the repeat hydrographic sections along 130°E, 137°E, 144°E and 155°E meridians, the hydrographic data from the Hawaii Ocean Time-series, the World Ocean Atlas 1994, and available gridded data of wind stress and evaporation. The classical idea that NPTW originates from the zone of the highest sea surface salinity at 20°–30°N centered around the international date line and spreads along the isopycnal geostrophic flow patterns is confirmed. Further, it is shown that the meridional extent of NPTW along 137°E is from 10°N to 23°N on average and the highest salinity core lies at about 15°N and 24.0σθ, and that the portion of NPTW north (south) of about 15°N originates from the formation region west (east) of the date line. NPTW in the 137°E section changed remarkably associated with the mid-1970s regime shift. North of 15°N NPTW increased both in its salinity and thickness while to the south of 15°N only its salinity increased and its thickness remained unchanged. The westward geostrophic velocity is increased significantly in both the southern and northern parts of NPTW. The northern thickening and speedup and the southern speedup increased NPTW transport across 137°E. The changes in the thermohaline forcing such as evaporation and Ekman salt convergence in the NPTW formation region possibly contributed to the increases in salinity in the southern part of NPTW, but not to that of the northern part. On the other hand, the increased Ekman pumping accounts for the increase of the NPTW inventory and transport at 137°E. The increased salinity of NPTW at 137°E, especially its northern portion, was presumably caused by an increase in its formation rate rather than changes in the sea surface salinity in its formation region; the thicker the NPTW layer is, the saltier is the core that tends to survive the mixing processes.