南海北部东沙岛以西陆坡区2021年秋季内波特征统计与分析

Characteristic statistics and analysis of internal waves in the continental slope area west of the Dongsha Plateau on the northern South China Sea in the autumn of 2021

本文利用2021年9-10月布放在南海北部东沙岛以西陆坡区的3套潜标观测数据分析了流花油田区内潮和内孤立波分布特征。调和分析显示,该海域正压潮流较弱,明显小于表底层斜压潮流。通过与全球潮汐模型对比发现,TPXO7.2对于半日分潮的模拟结果要明显优于全日分潮,模型结果低估了O1分潮,而高估了K1分潮的正压潮流振幅。调查海域斜压潮流表现为表底强化的第一斜压模态,O1分潮的斜压潮流椭圆振幅要大于K1分潮。观测期间,共有4次内孤立波群集中出现,且发生时间滞后于吕宋海峡天文大潮期3~4d。LH2站共记录了88个内波过程,其中内孤立波31个,内波波列57个,内波平均振幅31m。该站非线性内波过程集中出现于每日的4-6时、11-13时和18-20时,同时超过45%的单孤立子内波过程发生在4—6时。通过追踪9月8-12日共计5个内孤立波依次经过LH1、LH2和LH3站的传播过程,可以计算内波在LH1至LH2站位间的传播速度为1.23m·s^(-1),在LH2至LH3站位间的传播速度为1.77m·s^(-1),同时根据线性波动方程及Kdv方程计算其理论传播速度为1.55m·s^(-1)。本文的统计分析结果进一步加强了对典型秋季环境下南海北部流花油田区内波特征的理解和认识。

Observations from three moorings deployed in the continental slope area west of the Dongsha Plateau on the northern South China Sea(NSCS)from September to October 2021 are collected for the characteristic analysis of internal waves and internal solitary waves in the Liuhua oilfield area.Harmonic analysis shows the barotropic currents are obviously less than the baroclinic currents on the surface and bottom water layer.By comparison with the barotropic tidal currents obtained from TOPEX/Poseidon Global Inver Solution(TPXO7.2),it is found that the model results of semidiurnal tides are significantly better than that of diurnal tides,and the simulated results underestimate the current amplitude of O1 tidal constituent,but overestimate that of K1 tidal constituent.The internal tides show surface-bottom intensified baroclinic mode-1 structure,and the major axis of tidal ellipse of O1 tidal constituent is larger than that of K1.During the whole observation period,there are four internal solitary waves(ISWs)clusters passed by the Liuhua oilfield area in total,and the appearance time lags 3~4 days behind the astronomical spring tide of Luzon Strait.There are a total of 88 ISWs recorded at mooring of LH2,including 31 solitons and 57 ISW packets,and the averaged amplitude is 31 m.The daily appearance time for the ISWs concentrates between 4~6 am,11 am^(-1) pm and 6~8 pm,and more than 45%of solitons appears between 4~6 am.By tracking the propagation process passed by LH1,LH2 and LH3 of 5 ISWs appeared between 8~12 September,the calculated phase speed for the ISWs is 1.23 m·s^(-1) between LH1 and LH2 and 1.77 m·s^(-1) between LH2 and LH3,and the theoretical propagation speed is 1.55 m·s^(-1) based on the linear wave equation and Kdv equation.The statistical results in this paper further strengthen the understanding of the internal waves in the Liuhua oilfield area on the NSCS under the typical autumn environment.