Influence of North Pacific subtropical mode water variability on the surface mixed layer through the heaving of the upper thermocline on decadal timescales
Influence of North Pacific subtropical mode water variability on the surface mixed layer through the heaving of the upper thermocline on decadal timescales
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DOI：
10.1007/s10872-022-00677-y
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发表时间：
2023-01
影响因子：
2.3
通讯作者：
F. Kobashi;N. Usui;Nanami Akimoto;N. Iwasaka;T. Suga;E. Oka
中科院分区：
文献类型：
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作者：
F. Kobashi;N. Usui;Nanami Akimoto;N. Iwasaka;T. Suga;E. Oka
利用FORA-WNP 30年的四维变分海洋再分析资料，研究了北太平洋副热带模态水（STMW）的年代际变化及其对上层温跃层和混合层的影响。在年代际尺度上，黑潮延伸体以南的短时微波变化为冷/厚和暖/薄。这些变化被俯冲并平流到南部，在那里，厚（薄）的STMW导致上部温跃层在STMW上方上升（下降），在地下深处产生冷（暖）温度异常，在季节性温跃层的深处出现特别大的异常。除9月外，混合层在3 ~ 11月也出现温度异常。这些异常与STMW的温度异常具有相同的符号，尽管它们不是由于STMW在地表的重新出现，而是由于上部温跃层的隆起。在FORA-WNP 30中，由于混合层温度异常的形成主要是由于资料同化引入的增量，其机制尚不清楚。然而，混合层的热收支分析表明，夹带和/或垂直扩散的重要性，在混合层的底部，从上部温跃层的温度异常输送到混合层。STMW也影响混合层深度。厚（薄）STMW浅滩（加深）的季节性温跃层，增强（削弱）分层深度低于混合层，从而阻碍（有利于）混合层的发展，从7月至9月。
Decadal variability of the North Pacific subtropical mode water (STMW) and its influence on the upper thermocline and mixed layer are examined in a four-dimensional variational ocean re-analysis for the Western North Pacific over 30 years (FORA–WNP30). The STMW that forms south of the Kuroshio Extension becomes thick/cold and thin/warm on decadal timescales. These variations are subducted and advected to the south, where thick (thin) STMW causes the upper thermocline to heave up (down) above the STMW, producing cold (warm) temperature anomalies at subsurface depths, with especially large anomalies at the depths of the seasonal thermocline. Temperature anomalies also appear in the mixed layer from March to November, except in September. These anomalies have the same sign as the temperature anomalies of the STMW, although they are due not to the reemergence of the STMW at the surface but to the heaving of the upper thermocline. In the FORA–WNP30, because the formation of the mixed layer temperature anomalies owes much to the increment introduced by data assimilation, the mechanism remains unclear. A heat budget analysis of the mixed layer, however, suggests the importance of entrainment and/or vertical diffusion at the base of the mixed layer for conveying temperature anomalies from the upper thermocline to the mixed layer. The STMW also affects the mixed layer depth. A thick (thin) STMW shoals (deepens) the seasonal thermocline, enhancing (weakening) stratification at depths below the mixed layer and thus hindering (favoring) mixed layer development from July to September.