Decadal-scale variability of the North Pacific subtropical mode water and its influence on the pycnocline observed along 137°E
Decadal-scale variability of the North Pacific subtropical mode water and its influence on the pycnocline observed along 137°E
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DOI：
10.1007/s10872-020-00579-x
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发表时间：
2020-11
影响因子：
2.3
通讯作者：
F. Kobashi;Toshiya Nakano;N. Iwasaka;T. Ogata
中科院分区：
文献类型：
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作者：
F. Kobashi;Toshiya Nakano;N. Iwasaka;T. Ogata
通过分析日本气象厅(JMA)1972-2019年137°E经线的重复水文观测资料，分析了北太平洋副热带模水(STMW)的年代际变化及其对跃层的影响，重点分析了夏季STMW上方季节性上层跃层的发展。STMW出现在137°E的20°-32°N之间，厚度在十年时间尺度上变化，大约9-15年。ARGO浮子观测表明，观测到的STMW厚度变化源于前一年黑潮延伸部以南的冬季混合层。STMW对跃层有很大的影响。厚厚的STMW浅滩出现在上部的跃层上，偶尔伴随着下部主要跃层的加深。这种变化在上部跃层表现得很强烈，在那里等倾面的隆起伴随着地表附近的密度异常上升。次表层的副热带锋(STF)与上层跃层的北向浅滩有关，在气候学上由STMW维持，在年代际时间尺度上也有变化。一股较厚的短波加强了上跃层向北的浅海运动，加强了短时跃层。在年代际时间尺度上，STF的变化是由STMW引起的上跃层斜率的变化引起的。由模式水引起的STF的变化与以前数值模式的结果是一致的。
Decadal-scale variability of the North Pacific subtropical mode water (STMW) and its influence on the pycnocline are examined by analyzing Japan Meteorological Agency (JMA) repeat hydrographic observations along the 137°E meridian from 1972 to 2019, with a particular focus on the summer season when the seasonal upper pycnocline develops above the STMW. The STMW appears between 20° and 32°N at 137°E, with the thickness varying on decadal timescales of approximately 9–15 years. Argo float observations suggest that the observed change in the STMW thickness originates in the wintertime mixed layer south of the Kuroshio Extension in the preceding year. The STMW has a substantial impact on the pycnocline. The presence of thick STMW shoals the upper pycnocline, occasionally concurrent with the deepening of the lower main pycnocline. The change is robust in the upper pycnocline, where the heaving of isopycnal surfaces occurs with density anomalies up near the surface. The subtropical front (STF) at subsurface depths, which is associated with a northward shoaling of the upper pycnocline and is maintained by the STMW in the climatology, also changes on decadal timescales. A thick STMW increases the northward shoaling of the upper pycnocline and intensifies the STF. On decadal timescales, the STF variations are accounted for by the STMW-induced change in the upper pycnocline slope. The change in the STF due to mode waters is consistent with previous findings from numerical models.