海洋环流与波动重点实验室知识库

新几内亚沿岸流/潜流是来自南半球的水团跨越赤道向北太平洋输送的关键通道，在南北半球水交换中具有重要作用，自上世纪开始就有不少学者利用观测数据和模式数据对其结构和变化进行了分析。本文利用中国科学院海洋研究所2015年11月到2018年12月期间在142°E断面上0°、1°S、1.7°S三个站点的潜标观测数据对新几内亚沿岸流（New Guinea Coastal Current，NGCC）和新几内亚沿岸潜流（New Guinea Coastal Undercurrent，NGCUC）的多尺度变化进行了比较分析。潜标ADCP很好地观测到了新几内亚沿岸800m深度以上海流的季节内、季节及年际时间尺度变化，本文进一步结合OFES模式1980-2018年期间的输出数据对NGCC/NGCUC的年际变化规律及其与ENSO的关系进行了研究。主要结论如下：

（1）NGCC是一支上100m季节性逆转的海流，夏季向西北方向流动，8月份时在80m深度有向西的最大流速（约-55cm/s）；冬季向东南方向流动，2月份时在30m深度有向东的最大流速（约50cm/s）。次表层的NGCUC是一支在100-400m深度间稳定向西流动的海流，200m深度处存在向西的最大流速-39±10cm/s。NGCUC与NGCC的季节变化一致，夏季流速较强而冬季较弱，但其流向不随季节变化。400-800m之间的海流与NGCC有着相同的季节变化特点，其流向也会发生季节性的逆转。

（2）新几内亚沿岸300m以上的海流有明显的20-40天的季节内震荡。100m深度处的季节内信号最强，而且有向上传播和向下传播的趋势。分析表明：NGCC变化以季节信号为主导，季节信号和季节内信号的解释方差分别为48%和22%；而NGCUC变化则是以季节内信号为主导，其季节信号和季节内信号的解释方差分别为18%和67%。

（3）NGCC和NGCUC受到了沿岸季风的显著影响，夏季（boreal）期间，NGCC和NGCUC向西的流速均增强；冬季期间，NGCC向东南方向流动，而NGCUC向西的流速则明显减弱。800m以浅的海流与季风的相关系数大多在0.8-0.9之间，而且超过了95%的置信度，说明季风的强迫作用不止作用于300m，甚至可以影响到800m甚至更深的海流。值得注意的是，100-150m深度间的相关系数较低，这是由于100-150m之间存在着强烈的半年震荡导致的。

（4）NGCC/NGCUC还呈现出明显的年际变化，2015年11月至2016年6月厄尔尼诺期间表层的NGCC消失，而NGCUC占据了整个海洋上层，流核深度在50-100m之间，远浅于平均流核深度200m。在此期间，150m以上有向西的速度异常，而150m以下出现了向东的速度异常，这对应于NGCUC的流核深度变浅。2017年5月到2018年7月期间为ENSO冷相位，NGCUC的变化与2015/2016年厄尔尼诺期间的现象相反。OFES模式的合成结果表明NGCUC流核深度在厄尔尼诺期间会变浅，而在拉尼娜期间其流核深度会加深，而NGCUC的流量变化与ENSO无显著的相关性。

New Guinea Coastal Current (NGCC) and New Guinea Coastal Undercurrent (NGCUC) are key channels for the transport of water masses from the southern to the northern hemisphere. This paper uses the subsurface mooring data at the three sites of 0°, 1°S and 1.7°S on the section of 142°E off the New Guinea coast to examine the multi-scale variations of the NGCC and NGCUC. The mooring ADCP well observed the intraseasonal, seasonal and interannual variations of the currents above 800m off the coast of New Guinea from November 2015 to December 2018. The main conclusions are as follows:

(1) NGCC is a seasonally reversing current in the upper 100m. It flows northwestward in the summer (boreal). In August, it has a maximum westward velocity (about -55cm/s) at the depth of 80m. In winter, it flows southeastward. In February, there is a maximum eastward velocity (about 50cm/s) at the depth of 30m. The NGCUC in the subsurface layer is a current that flows stably westward in the depth range of 100-400m, and a maximum westward velocity of -39±10cm/s exists at the depth of 200m. The seasonal variations of NGCUC are similar to that of NGCC. Its velocity is stronger in summer and weaker in winter, but its direction does not change with season. The current between 400-800m also has similar seasonal cycle as the NGCC, and its direction reverses with season.

(2) The currents in the upper 300m along the coast of New Guinea have obvious intraseasonal variations with period of 20-40 days. The signal at the depth of 100m is the strongest, and there is a signal to propagate upward and downward. Further analysis shows that: NGCC is dominated by seasonal signals, and the interpretation variance of seasonal signals and intra-season signals are 48% and 22%, respectively; while NGCUC is dominated by intraseason signals, and its interpretation variances of seasonal signals and intra-season signals are 18% and 67%, respectively.

(3) NGCC/NGCUC are significantly affected by the coastal monsoon. In summer (boreal), the westward velocity anomalies are enhanced. In winter, the NGCC flows to the southeast and the westward NGCUC is obviously weakened. The correlation coefficients between the currents above 800m and monsoon are mostly between 0.8-0.9, and all exceed the 95% confidence level, which shows that the monsoon's forcing effect not only affects 300m, but also affects 800m or deeper currents. It is worth noting that the correlation coefficient between the depth of 100-150m is low, which is caused by the strong semi-annual oscillation.

(4) NGCC/NGCUC also show significant interannual variations. From November 2015 to June 2016, the surface NGCC disappeared, and NGCUC occupied the entire upper layer of the ocean, and the depth of the current core was between 50-100m, shallower than the mean core depth of 200m. During this period, there were a westward velocity anomaly above 150m and an eastward velocity anomaly below, which corresponds to the shoalling of the NGCUC. During the cold phase of ENSO from May 2017 to July 2018, the variation of NGCUC is opposite to that during El Niño in 2015/2016. Analysis with OFES model show that the depth of the NGCUC velocity core becomes shallow during El Niño, and deepen during La Niña, and the transport of NGCUC appears no significant correlation with ENSO.