Properties of winter mixed layer variability on the shelf-slope region facing the Kuroshio―study of Tosa Bay, southern Japan
Properties of winter mixed layer variability on the shelf-slope region facing the Kuroshio―study of Tosa Bay, southern Japan
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面向黑潮的陆架斜坡区域冬季混合层变化特征——日本南部土佐湾的研究
DOI：
10.1007/s10236-013-0670-9
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发表时间：
2014
期刊：
影响因子：
2.3
通讯作者：
Tomowo Watanabe
中科院分区：
文献类型：
--
作者：
Hiroshi Kuroda;Yuichi Hirota;Takashi Setou;Kazuhiro Aoki;Daisuke Takahashi;Tomowo Watanabe
为了研究黑潮陆架坡水域冬季混合层的变化特征，我们分析了历史温度记录和一个三嵌套的高分辨率数值模式的模拟结果。作为陆架斜坡水域的候选者，我们把重点放在了日本南部近海的托萨湾。观测到的月平均ML温度和海湾深度的时间序列显示出显著的季节变化。ML的发展可分为两个阶段：9~11月，海面冷却逐渐加强，ML温度和深度分别减小和增加；1~3月，ML温度和深度基本不变，1月海面冷却达到年最大值。在后者中，月平均ML深度的变化是一年中最大的。为了进一步研究对应于冬季的后一种情况下的ML特性，我们对模拟结果进行了检验。结果发现，ML深度的最大方差归因于一个显性的月内变化。这与黑潮及其锋面扰动引起的具有10-20公里典型空间尺度的亚中尺度变化有关。模拟的ML内月平均热量平衡表明，热量平流与海面热通量和通过ML底部的夹带相平衡。此外，月平均热量平流主要由月内涡动热量平流决定，这表明与亚中尺度变化相关的高频月内变化对冬季ML的低频月变化有重要贡献。
To examine the properties of winter mixed layer (ML) variability in the shelf-slope waters facing the Kuroshio, we analyzed historical temperature records and the simulated results of a triply nested high-resolution numerical model. As a candidate of the shelf-slope waters, we focused on Tosa Bay, off the southern Japan. A time series of observed monthly mean ML temperatures and depths in the bay exhibits a remarkable seasonal variation. The period when the ML develops can be divided into two regimes: from September to November, when the sea surface cooling is gradually enhanced, the ML temperature and depth decreases and increases, respectively; from January to March, the ML temperature and depth are kept nearly constant, while the sea surface cooling in January reaches its annual maximum. In the latter regime, variance for the monthly mean ML depth is the largest of the year. To further study the ML properties in the latter regime corresponding to winter, we examined simulated results. It was found that the largest variance for ML depth is attributed to a dominant intramonthly variation. This is related to a submesoscale variation with typical spatial scales of 10–20 km, induced by the Kuroshio and its frontal disturbances. Simulated monthly mean heat balance within the ML showed that heat advection balances with heat flux at the sea surface and entrainment through the ML bottom. Moreover, the monthly mean heat advection is determined mainly by the intramonthly eddy heat advection, suggesting that the high-frequency intramonthly variation related to submesoscale variations contributes significantly to the low-frequency monthly variations of the ML in winter.