基于夏季船载ADCP数据的台湾海峡西南部平均流与潮流特征的初步研究

Study on characteristics of mean flow and tidal currents in the southwestern Taiwan Strait based on shipboard ADCP observations in summertime

文章采用国内外普遍适用于船载声学多普勒流速剖面仪(shipboard acoustic doppler current profilers,SADCP)数据滤潮处理的时空拟合最小二乘法(简称最小二乘法),对台湾海峡南部浅滩2004—2013年夏季(6—9月)所获取的SADCP数据进行正压潮、流分离。结果表明:最小二乘法获得的平均流和基于原始数据格点化后矢量平均取得的平均流流向均趋于东北向,并且具有大致相同的强、弱流区空间分布形态,但最大流速稍有差异,分别为0.48m×s^(-1)和0.36m×s^(-1);此外,强流区(流速~0.3m×s^(-1))流幅狭窄,流轴分别约束在东山至龙海外海30m等深线附近和台湾浅滩南部地形骤变区域;而弱流区(流速<0.1cm×s^(-1))集中分布于台湾浅滩中部。进一步研究表明,2种平均流所估算的海流通量的计算结果比较接近,可达到(0.74±0.25)×10~6m^3·s^(-1)。SADCP数据分离所得M_2分潮流显示:台湾浅滩至东山一线为强潮区,最大可能流速出现在台湾浅滩(约0.67m×s^(-1));等潮时线分布符合前进波特征,在潮波传导方向上由西南向东北依次推迟(约2h);东山近海存在一条呈NW—SE走向的椭圆率正负分界线,分界线以南潮流椭圆顺时针旋转,以北则逆时针旋转。

In this study,we conducted barotropic detiding of the summertime shipboard ADCP（SADCP） dataset in the southern Taiwan Strait（TWS） from June to September during 2004-2013,employing the widely used spatiotemporal fitting by the least squares method（STF-LSM）.The results show that the mean flow derived from STF-LSM and that derived from averaged vectors by dataset gridding both flowed northeastward.Moreover,these two mean flows had similar spatial distribution patterns of strong and weak flows,but their maximum velocities were slightly different：0.46 and 0.34 m·s^-1 for the former and the latter,respectively.Besides,the strong currents（about 0.3 m·s^-1） were characterized by the narrow mainstream confined around the depth of 30 m off the sea at Dongshan and Longhai as well as the Taiwan Bank（TWB） with drastic topographic change,whereas the weak currents（less than 0.1 m·s^-1） were mainly distributed in the central TWB.Estimation of the volume transport based on the above mentioned mean flows revealed similar results,up to（0.71±0.24） ×10~6 m^3·s^-1.The strong M2 tidal currents derived from SADCP were near the TWB and extended to the offshore of Dongshan,with a maximum M2 current amplitude as large as ~0.64 m·s^-1,which was located in the TWB.The cotidal chart for M2 currents demonstrates the characteristics of progressive wave,which was delayed successively from the southwest to the northeast along the direction of the tidal wave as the wave propagated（about 2 h）.Besides,there was a boundary line along northwestward to southeastward direction with ellipticity equal to zero at the offshore of Dongshan.The M_2 currents rotated counterclockwise in the southern region of this boundary line and clockwise in the northern region.