西北太平洋跨等密度面湍流混合的时空变化分析

ANALYSIS OF TEMPORAL-SPATIAL VARIATIONS OF TURBULENT DIAPYCNAL MIXING IN THE NORTHWESTERN PACIFIC

基于细尺度参数化方法,利用2000—2007年的历史水文剖面资料,分析了西北太平洋海区(135°—180°E,25°—45°N)跨等密度面湍流混合的时空分布特征。结果表明,垂直平均的耗散率与地形粗糙度的空间分布基本一致,且随经度自西向东减弱。在地形粗糙的地方,耗散率达O(10–8m2/s3),而在地形平坦的地方,耗散率仅O(10–11m2/s3)。另外,上层海洋混合存在明显的季节变化,在日本近岸的海区,耗散率冬季最强而夏季最弱,与风生近惯性能量之间存在显著的正相关;在大洋内区,耗散率冬季最强而秋季最弱,与风生近惯性能量的相关关系较弱。进一步地,本文分析了风应力在不同海区对混合的影响深度,结果显示在伊豆-小笠原海脊以西,风应力的影响深度最浅为620m,而在该海脊以东最深可达1740m。

Based on historical hydrographic data of 2000—2007, temporal and spatial variations of turbulent diapycnal mixing in the northwestern Pacific are evaluated by employing a fine-scale parameterization method. In general, the spatial distribution of vertically averaged dissipation rate is consistent with topography along with a decreasing tendency from west to east. The estimated mean value is about O(10–8 m2/s3) over rough topography, and O(10–11m2/s3) on smooth seafloor. The turbulent mixing in the upper ocean in flat bathymetry also displays a distinct seasonal variability. It is found that the dissipation rate near shore is the strongest in winter and weakest in summer, which agrees well with the wind-induced near-inertial energy flux. In the ocean interior, however, the dissipation rate is the strongest in winter and weakest in fall, bearing a rather weak correlation with wind work on near-inertial motions. In addition, the vertical extent for wind stress exerting effects on turbulent mixing in different regions is estimated. It shows that the wind penetration depth is the shallowest west of the Izu-Ogasawara Ridge with a value of 620 m and deepest east of this ridge with a value of 1740 m.