Decadal variability in the formation of the North Pacific Subtropical Mode Water: Oceanic versus atmospheric control
Decadal variability in the formation of the North Pacific Subtropical Mode Water: Oceanic versus atmospheric control
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DOI：
10.1175/jpo2918.1
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发表时间：
2006-07-01
影响因子：
3.5
通讯作者：
Chen, Shuiming
中科院分区：
文献类型：
--
作者：
Qiu, Bo;Chen, Shuiming
利用原位温度和测高海面高度资料研究了过去12年北太平洋副热带模态水（STMW）形成的低频变化。在STMW形成的黑潮延伸（KE）再环流环流内，主导信号的特征是1993 - 1999年冬末混合层深度和16 -18℃恒温层深度逐渐变薄，2000年以后这些特征逐渐变厚。同样的年代际信号也出现在再环流以南的副热带内部环流的低势涡（PV） STMW层。通过分析NCEP-NCAR再分析项目的海气通量数据，发现年代际STMW信号与冬季地表累积冷却的年际变化相关性不大。相反，发现年代际信号与KE系统动态状态的变率密切相关。具体而言，当KE路径处于变状态时，STMW的形成减少，在此期间，高区域涡变率将高pv KE水注入再循环环流，增加了上层海洋分层，阻碍了深冬混合层的发展。另一方面，稳定的KE路径有利于弱分层的维持，导致冬季深层混合层和厚STMW层的形成。利用简单的上层海洋热保持模式和整体混合层模式量化了表层海气通量强迫与预处理分层在控制冬末混合层深度变化中的相对重要性。发现大部分方差（接近80%）是由于KE系统动态状态控制的分层变化。
In situ temperature and altimetrically derived sea surface height data are used to investigate the low-frequency variations in the formation of the North Pacific Ocean Subtropical Mode Water (STMW) over the past 12 yr. Inside the Kuroshio Extension (KE) recirculation gyre where STMW forms, the dominant signal is characterized by a gradual thinning in the late winter mixed layer depth and in the 16 degrees-18 degrees C thermostad layer from 1993 to 1999 and a subsequent steady thickening of these features after 2000. This same decadal signal is also seen in the low-potential-vorticity (PV) STMW layer in the interior subtropical gyre south of the recirculation gyre. By analyzing the air-sea flux data from the NCEP-NCAR reanalysis project, little correlation is found between the decadal STMW signal and the year-to-year changes in the cumulative wintertime surface cooling. In contrast, the decadal signal is found to be closely related to variability in the dynamic state of the KE system. Specifically, STMW formation is reduced when the KE path is in a variable state, during which time high regional eddy variability infuses high-PV KE water into the recirculation gyre, increasing the upper-ocean stratification and hindering the development of a deep winter mixed layer. A stable KE path, on the other hand, favors the maintenance of a weak stratification, leading to a deep winter mixed layer and formation of a thick STMW layer. The relative importance of the surface air-sea flux forcing versus the preconditioning stratification in controlling the variations in the late winter mixed layer depth is quantified using both a simple upper-ocean heat conservation model and a bulk mixed layer model. The majority of the variance (similar to 80%) is found to be due to the stratification changes controlled by the dynamic state of the KE system.