Seasonal variations in salinity of the North Pacific Intermediate Water and vertical mixing intensity over the Okinawa Trough
Seasonal variations in salinity of the North Pacific Intermediate Water and vertical mixing intensity over the Okinawa Trough
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DOI：
10.1007/s10872-020-00585-z
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发表时间：
2021-01
影响因子：
2.3
通讯作者：
Hirohiko Nakamura;R. Inoue;A. Nishina;Toshiya Nakano
中科院分区：
文献类型：
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作者：
Hirohiko Nakamura;R. Inoue;A. Nishina;Toshiya Nakano
利用2013年世界海洋地图集和冲绳海槽历史电导率、温度和深度数据，利用北太平洋中层水（NPIW）盐度的季节变化，推导了北方冲绳海槽中层垂直混合强度的季节变化。用简单的平流模式对NPIW的水团分析表明，冬季中间层的垂直混合强度以年平均振幅值的20-50%的速率增强。为了确定垂直混合的季节变化背后的驱动力，我们检查了2004-2011年期间北方冲绳海槽的系泊海流计数据，并表明在1月份左右，在大陆坡黑潮下方，中间层的近惯性内波能量增强;这是由于冬季与深气旋涡旋发展相关的强烈西南气流。我们使用的密度和速度数据从一个现实的高分辨率海洋环流模式模拟假设，大振幅黑潮曲流和相关的深气旋涡在冬季产生近惯性内波通过离心/惯性不稳定性的负位涡，不仅出现在黑潮附近的西坡，但也附近的槽的东坡。此外，沿近海黑潮锋的沿着对称不稳定性和冬季的风能输入被认为是冬季增强的中间层近惯性内波能量的可能来源。
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.