Formation Mechanism of Barrier Layer in the Subtropical Pacific
Formation Mechanism of Barrier Layer in the Subtropical Pacific
复制标题
副热带太平洋屏障层的形成机制
DOI：
10.1175/jpo-d-15-0028.1
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发表时间：
2015
影响因子：
3.5
通讯作者：
Kanako Sato
中科院分区：
文献类型：
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作者：
Shota Katsura;Eitarou Oka;Kanako Sato
利用2003- 2012年的Argo剖面浮标资料和网格化资料、各种通量资料以及世界海洋环流实验水文计划的水文剖面资料，研究了副热带南北太平洋障碍层的季节和年际变化及其形成机制。由原始Argo剖面检测到的BL存在于位于SSS最大值赤道侧的海表盐度（SSS）锋内，冬季最厚，最频繁，时间尺度短于10天，表明其瞬变性质。对前人研究提出的BL形成的地表和地下过程进行了评价。向极Ekman平流的淡水占主导地位的表面清新过程，但不能解释所观察到的季节变化的BL。高盐度热带水向赤道方向的次表层侵入太深，在等温层内不会产生盐度分层。这些结果表明，副热带太平洋边界层的形成主要是由于近海面的向极Ekman气流和次表层的向赤道地转气流共同作用，使SSS锋倾斜而形成的。这一想法是支持的主导贡献的纬向SSS梯度纬向海面密度梯度内的SSS前和BL和等温层深度的季节变化之间的对应关系。在年际时间尺度上，北太平洋和南太平洋冬季边界层厚度分别与太平洋年代际振荡和厄尔尼诺-南方涛动有关，信风强度通过控制等温层厚度而起作用。
Seasonal and interannual variations of the barrier layer (BL) and its formation mechanism in the subtropical North and South Pacific were investigated by using raw and gridded Argo profiling float data and various surface flux data in 2003–12 and hydrographic section data from the World Ocean Circulation Experiment Hydrographic Programme. BLs detected by raw Argo profiles, which existed within the sea surface salinity (SSS) front located on the equator side of SSS maxima, were thickest and most frequent in winter and had a temporal scale shorter than 10 days, indicating their transient nature. Surface and subsurface processes for the BL formation suggested by previous studies were evaluated. Poleward Ekman advection of fresher water was dominant as the surface freshening process but cannot explain the observed seasonal variations of the BL. Subsurface equatorward intrusion of high-salinity tropical water was too deep to produce salinity stratification within isothermal layers. These results strongly suggest that BLs in the subtropical Pacific are formed mainly through tilting of the SSS front due to the poleward Ekman flow near the sea surface and the equatorward geostrophic flow in the subsurface. This idea is supported by the dominant contribution of the meridional SSS gradient to the meridional sea surface density gradient within the SSS front and the correspondence between the seasonal variations of the BL and isothermal layer depth. On an interannual time scale, the winter BL thickness in the North and South Pacific was related to the Pacific decadal oscillation and the El Niño–Southern Oscillation, respectively, through the intensity of trade winds controlling isothermal layer depth.