Low frequency variation of abyssal current east of the Luzon Strait: Cast study from in situ observation
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摘要: 本文利用在菲律宾海布放的一套锚系潜标获取的长时间海流和水温观测数据，分析了吕宋海峡以东的深海海洋环境特征，着重阐释了该海域海流的全水深垂向结构及其低频变化特征。研究表明，表层(100～160 m)平均流向为西偏北，流速约为12.5 cm/s；中层(810 m)的平均流为西向，流速为2.6 cm/s；深层(1 550 m和2 560 m)的平均流速在1 cm/s以内，近底(4 040 m)的流向为较稳定的西南向，流速为2.3 cm/s。上层海流的动能比中层和深层大1～2个量级，总动能、平均动能、涡动动能均在表层最大，中层次之、深层最小，各层次涡动能均大于平均动能。中上层海流的低频变化具有极高的相似性，全年为81～85 d的周期振荡；近底层海流则不同，变化周期约为51 d。Abstract: In order to investigate long-term variations of deep sea currents and temperature in the east of the Luzon Strait, a submarine mooring system was made at 19.75°N, 126.75°E from May 2015 to May 2016 in the Philippine Sea. The vertical distribution of ocean currents and its temporal variation characteristics are analyzed in the paper. Several features show that: (1) In the upper layer (100～160 m) , the average current velocity is about 12.5 cm/s with average flow direction oriented northwest; in the middle layer (810 m), the average current velocity is about 2.6 cm/s with flow direction oriented westward; in the deep layer of 1 550 m and 2 560 m, the average current velocity is small and less than 1 cm/s whereas that in 4 040 m is about 2.3 cm/s and oriented southwest. (2) The kinetic energy of the upper layer is one to two orders of magnitude compared with the middle and the deep layers. In the deep layer, the total kinetic energy and average kinetic energy in the 4 040 m layer is the largest, with smallest total kinetic energy and eddy kinetic energy in the 2 560 m layer, and with smallest averaged kinetic energy and largest eddy kinetic energy in the 1 550 m layer. Meanwhile, eddy kinetic energy is larger than averaged kinetic energy in all the layers. (3) The wavelet analysis shows that ocean current exhibits a low-frequency oscillation period of 81～85 d in layers shallower than 2 560 m, while the current at 4 040 m shows 51 d oscillation period.
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Key words:
- full water depth /
- submarine mooring /
- low frequency variation /
- the Luzon Strait /
- the Philippine Sea
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图 1 潜标位置(a)、区域水深(b)、潜标所在断面水温及观测层次(c)和气候态风场(d)
Fig. 1 Location of the mooring (a), water depth around the mooring (b), temperature of section 126.75°E and observation layers of the mooring (c), and climatologic monthly winds at the mooring position (d)
图 2 日均（a）和月均（b）潜标观测各层次海流矢量时间序列
Fig. 2 Daily averaged (a) and monthly averaged (b) time series of observed current vectors
图 3 潜标观测各层次年均海流矢量
Fig. 3 Annually averaged current vectors at different layers observed by mooring
图 5 各层次海流平均动能和涡动动能季节变化
Fig. 5 Seasonal variation of average kinetic energy and eddy kinetic energy at different layers
图 6 垂向平均海流和水温频谱分析
Fig. 6 Frequency-spectrum of vertically averaged current and temperature
图 7 各层次经向流速(a−e)、水温(f−j)小波分析
填色图为小波功率谱，曲线图为全球小波谱。填色图中粗黑线包围的范围通过了p=0.05显著性水平下的红噪声标准谱的检验；细黑线为影响锥曲线，在该曲线以外的功率谱由于受到边界效应的影响而不予考虑
Fig. 7 Wavelet analysis of meridional currents (a−e) and temperature (f−j) at different layers
The color filled maps represent wavelet power spectrum and the curves on the right represent global wavelet spectrum. In the color maps, the thick black contours denote the 5% significance level against red noise. The cone of influence where edge effects might distort the picture is shown in lighter shades
表 1 各层次海流及动能年平均统计值(3 d低通滤波后计算)
Tab. 1 Statistics of currents and kinetic energy at different layers (calculated after 3 d averaged)
水深/m 平均流速
/cm·s−1平均流向/（°） 最大流速
/cm·s−1平均水温/℃ 总动能
/cm2·s−2平均动能
/cm2·s−2平均动能占总动能
百分比/%涡动动能
/cm2·s−2涡动动能占总动能
百分比/%100 12.5 281 55 − 358.78 77.98 22 280.80 78 160 12.4 282 41 20.36 232.93 77.27 33 155.66 67 810 2.6 270 12 5.00 15.08 3.36 22 11.72 78 1 550 0.3 178 6 2.64 4.85 0.03 1 4.81 99 2 560 0.6 224 6 1.76 2.12 0.20 9 1.92 91 4 040 2.3 209 10 1.59 5.64 2.54 45 3.10 55 注：−表示缺测数据。 
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表 2 3～120 d带通滤波各变量时间变化的显著周期(单位：d)
Tab. 2 Significant periods (unit: d) of meridional current and temperature (3～120 d filtered)
水深/m 经向流速 水温 100 81 − 160 82 76 810 85 84 1 550 84 84 2 560 84 84 4 040 51 90 注：−表示缺测数据。
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