Seasonal variations in vertical mixing intensity in the intermediate layer of the northern Okinawa Trough was deduced using the seasonal variations in salinity in the North Pacific Intermediate Water (NPIW) using two distinct datasets: the World Ocean Atlas 2013 and historical conductivity, temperature, and depth data in the Okinawa Trough. Water mass analysis of the NPIW with a simple advection model showed that the vertical mixing intensity in the intermediate layer is enhanced in the winter at a rate of 20–50% of the annual mean amplitude value. To determine the driving force behind the seasonal variations in vertical mixing, we examined moored current-meter data in the northern Okinawa Trough during 2004–2011 and showed that the near-inertial internal wave energy in the intermediate layer was enhanced around January beneath the Kuroshio on the continental slope; this was due to strong southwestward flows associated with deep cyclonic eddies developing in the winter. We used density and velocity data from a realistic high-resolution ocean general circulation model simulation to hypothesize that the large-amplitude Kuroshio meander and associated deep cyclonic eddies in the winter generate near-inertial internal waves through centrifugal/inertial instability in the area of negative potential vorticity that appears not only beneath the Kuroshio near the western slope but also near the eastern slope of the trough. In addition, the symmetric instability along the offshore Kuroshio front and the wind energy input in the winter are suggested as possible sources of winter-enhanced near-inertial internal wave energy in the intermediate layer.

中文翻译：

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冲绳海槽北太平洋中水盐度的季节性变化和垂直混合强度

使用北太平洋中层水 (NPIW) 盐度的季节性变化，使用两个不同的数据集推断冲绳海槽北部中间层垂直混合强度的季节性变化：2013 年世界海洋地图集和历史电导率、温度和深度冲绳海槽数据。使用简单平流模型对 NPIW 进行的水质量分析表明，冬季中间层的垂直混合强度以年平均振幅值的 20-50% 的速度增强。为了确定垂直混合季节性变化背后的驱动力，我们检查了 2004 年至 2011 年期间冲绳海槽北部的系泊电流计数据，表明中间层的近惯性内波能量在 1 月左右在大陆坡黑潮下方增强；这是由于与冬季形成的深层气旋涡旋相关的强烈西南流。我们使用来自真实高分辨率海洋环流模型模拟的密度和速度数据来假设冬季的大振幅黑潮曲流和相关的深气旋涡流通过负区域的离心/惯性不稳定性产生近惯性内波。潜在涡度不仅出现在西坡附近的黑潮下方，而且出现在槽的东坡附近。此外，