Elevated Mixing Estimates and Trapped Near-Inertial Internal Waves on the Inshore Flank of the New Guinea Coastal Undercurrent From Sustained Glider Observations in the Solomon Sea

IF 3.3 2区 地球科学 Q1 OCEANOGRAPHY
T. M. Shaun Johnston, Daniel L. Rudnick, William S. Kessler
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Abstract

The Solomon Sea is a major contributor to (a) the volume transport into the Equatorial Undercurrent and (b) the associated heat transport, which has an order one effect on interannual temperature variability on the equator according to previous work. The narrow western boundary current (New Guinea Coastal Undercurrent, NGCU) merges with the broad, shallow North Vanuatu Jet within 100 km of the southern entry to the sea, which implies mixing. Existing estimates from observations suggest mixing is larger than in models with different mixing parameterizations, which produce disparate properties of these exiting waters. Here, we use sustained underwater glider measurements across the Solomon Sea from 2007 to 2020 to examine the spatial variability of mixing estimates and internal waves. We estimate diffusivity via a finescale parameterization using the vertical strain of isopycnal displacements from internal waves. A typical accuracy of this parameterization when compared to turbulence measurements is within a factor of 2–3. Our results and previous observations in this area agree within this factor. Our main results are: (a) vertical diffusivity estimates are about 10 4 ${10}^{-4}$   m 2 ${\mathrm{m}}^{2}$   s 1 ${\mathrm{s}}^{-1}$ on the inshore, anticyclonic side of the NGCU, which are 10–100 times higher than offshore and (b) elevated near-inertial internal wave (NIW) amplitudes are also found inshore. Taken together, these results suggest trapping of NIW by the anticyclonic vorticity of the NGCU leads to the elevated mixing within 100 km of the entry to the Solomon Sea.

从所罗门海持续滑翔机观测得出的新几内亚海岸暗流近岸侧的混合估算值升高和近惯性内陷波
所罗门海是(a)进入赤道暗流的体积输送和(b)相关热量输送的主要来源,根据以前的工作,热量输送对赤道的年际温度变化具有一阶影响。狭窄的西部边界流(新几内亚沿岸暗流,NGCU)在南部入海处 100 公里范围内与宽而浅的北瓦努阿图喷流汇合,这意味着混合。现有的观测结果表明,混合的程度大于采用不同混合参数的模式,而这些模式会产生不同性质的出海水域。在此,我们利用 2007 年至 2020 年对所罗门海的持续水下滑翔机测量来研究混合估计值和内波的空间变化。我们利用内波等距位移的垂直应变,通过精细参数化估算扩散率。与湍流测量结果相比,这种参数化的典型精度在 2-3 倍以内。我们的结果与之前在这一领域的观测结果一致。我们的主要结果是(a) NGCU 沿岸反气旋一侧的垂直扩散率估计值约为 10 - 4 ${10}^{-4}$ m 2 ${\mathrm{m}}^{2}$ s - 1 ${\mathrm{s}}^{-1}$ ,比离岸高 10-100 倍;(b) 沿岸也发现近惯性内波(NIW)振幅升高。总之,这些结果表明,近惯性内波被 NGCU 的反气旋涡度捕获,导致进入所罗门海 100 公里范围内的混合程度升高。
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来源期刊
Journal of Geophysical Research-Oceans
Journal of Geophysical Research-Oceans Earth and Planetary Sciences-Oceanography
CiteScore
7.00
自引率
13.90%
发文量
429
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