Diagnosing the development of seasonal stratification using the potential energy anomaly in the North Pacific
Diagnosing the development of seasonal stratification using the potential energy anomaly in the North Pacific
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DOI：
10.1007/s00382-019-04816-y
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发表时间：
2019-05
期刊：
影响因子：
4.6
通讯作者：
R. Yamaguchi;T. Suga;K. Richards;B. Qiu
中科院分区：
文献类型：
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作者：
R. Yamaguchi;T. Suga;K. Richards;B. Qiu
海洋上层季节性分层（季节性斜斜和/或过渡层）是一个普遍存在的特征，其垂直结构具有较大的空间变异性。密度分层调节上层海洋的稳定性，从而通过调节垂直混合影响海洋对大气强迫和生物地球化学过程的响应。在这项研究中，我们使用基于Argo剖面的势能异常（PEA）作为度量，从水柱稳定性的角度描述了季节性分层的发展。PEA收支分析显示，在北太平洋的大部分地区，季节性分层是在垂直一维能量平衡下发展的，在垂直一维能量平衡下，由大气浮力强迫驱动的PEA增加（即分层加强）和与水柱内垂直混合相关的PEA减少。只有在10°N以南的西边界流和赤道流系统区域，PEA水平平流对分层的季节发展起着重要作用。我们发现，除了海洋浮力增益的总幅度外，大气强迫（非穿透性地表浮力强迫和穿透性辐射加热）组成之间的平衡对于解释季节分层发展的区域差异也很重要。从PEA收支残差估计的季节分层垂直扩散系数在5 × 10−5m2s−1到5 × 10−4m2s−1之间，并显示与局地风强迫相关的空间和季节变化。
Upper-ocean seasonal stratification (seasonal pycnocline and/or transition layer) is a ubiquitous feature and its vertical structure has large spatial variability. The density stratification regulates the stability of the upper ocean and thus can affect the oceanic response to atmospheric forcing and biogeochemical processes by modulating vertical mixing. In this study, we described the development of the seasonal stratification in terms of the stability of the water column, using the potential energy anomaly (PEA) as a metric based on Argo profiles. PEA budget analysis reveals that over most of the North Pacific, seasonal stratification develops under a vertical one-dimensional energy balance between an increase in PEA (i.e., a strengthening of the stratification) driven by atmospheric buoyancy forcing and a decrease in PEA associated with vertical mixing within the water column. Horizontal advection of PEA plays a significant role in the seasonal development of the stratification only in the regions of the western boundary current and equatorial current system south of 10°N. We find that, in addition to the total magnitude of the oceanic buoyancy gain, the balance between compositions of the atmospheric forcing (non-penetrating surface buoyancy forcing and penetrating radiative heating) is also important in explaining regional differences in the development of the seasonal stratification. The vertical diffusivity in the seasonal stratification estimated from the residual of the PEA budget is in the range from 5 × 10−5m2s−1to 5 × 10−4m2s−1and shows spatial and seasonal variability associated with local wind forcing.