摘要:
基于2002年春季航次在吕宋海峡海域锚碇测流站(20°49'57"N,120°48'12"E)200,500与800m锚碇测流水层观测流,进行的海流特征分析与最大熵方法谱分析,得到以下主要结果.(1)在200m处,观测期间海流平均速度为(47.4cm/s,346°),最大观测海流速度Vmax和最大日平均海流速度Vd,max分别为(103.8cm/s,10°)和(71.6cm/s,339°);在500m处,观测期间平均流速为(20.3cm/s,350°),最大观测海流速度Vmax和最大日平均海流速度Vd,max分别为(74.1cm/s,17°)和(39.1cm/s,317°).这些都表明黑潮在吕宋海峡锚碇测流站200和500m处向西北方向入侵南海.(2)在800m处,观测期间平均流速为(1.2cm/s,35°),最大观测海流速度Vmax和最大日平均海流速度Vd,max分别为(10.8cm/s,76°)和(4.7cm/s,46°).这些都表明,它们的流向皆为东北向.比较在每层实测流的结果,表明在800m层海流状况与200和500m层海流状况是不相同的,流速随深度变深明显减弱,流向向右偏转.(3)在观测期间200,500和800m处,日平均流速在4月皆比3月时要强.(4)在200～800m潮流随深度变深有所变化,除了在500m处f<0情况全日潮峰值高于半日潮峰值以及对于半日潮以逆时针方向为主以外,其余情况在200～800m水层半日潮峰值都要高于全日潮的峰值,并且皆以顺时针方向旋转为主.(5)在200～800m水层都存在15d以上或14d左右的周期振动,例如在逆时针方向分量谱(f>0)在200,500m处存在19d左右的周期振动;在800m处存在14d左右的周期振动(f<0).(6)在200～800m处都存在4～6d周期天气过程的振动和2～3d周期振动.还都存在34.5h左右惯性振动周期,它的振动方向为顺时针方向.(7)通过交叉谱的计算,揭示:1)200与500m层两组流速时间序列对于半日潮周期、全日潮周期、15d以上的周期振动、2～3d的周期振动等都有很好的相关性,且对15d以上的长周期振动几乎是同步的;2)500与800m层两组流速时间序列对于4～6d天气过程的周期振动与2～3d的周期振动等都有很好的相关性,但它们之间有相位差,有滞后或提前现象.
Abstract:
On the basis of the current measurements at 200,500 and 800 m from moored current meters with the time series data from March 17 to April 15 at the mooring station(20°49'57"N,120°48'12"E) in Luzon Strait during spring of 2002 cruise,the spectral analy ses and calculation have been made.The major observed results are as follows:(1) the average velocity in the observing days is(47.4cm/s,346°) at the 200 m levels.The maximum observed current velocity Vmax and maximum daily current velocity Vd,max are(103.8 cm/s,10°) and(71.6 cm/s,339°) at 200 m level,respectively.The averag evelocity in the observing days is(20.3 cm/s,350°) at the 500 m level.Vmax and Vd,max are(74.1 cm/s,17°) and(39.1 cm/s, 317°) at 500 m level,respectively.The above results mean that the Kuroshio intrudes north west ward at the 200 and 500 m levels of moored station through the Luzon Strait in SCS.(2) The average velocity in the observing days is(1.2 cm/s,35b) at the 800 m level.Vmax and Vd,max are(10.8 cm/s,76°) and(4.7 cm/s,46°) at 800 m level,respectively.i.e.,their directions are north east ward.This means that the flow condition at the 800 m levels very differs from that at the 200 and 500 m levels,and their velocities decease with depth and their directions rotate clockwise with the change of depth.(3) The currents are stronger in April than these in March.(4) There exists the prominent fluctuations of tidal current.There exists also variation of tidal current with the change of depth.At 200,500 and 800 m levels,the semidiurnal peak is higher than the diurnal peak and the clockwise component is dominant in their fluctuations except for the height of diurnal peak is higher than that of semidiurnal peak for the clockwise component and the count erclockwise component is dominant in their fluctuations for semidiurnal peak at the 500 m level.(5) There is the prominent fluctuation of period of more than 15 d or about 14 d at the 200,500 and 800 m levels.For example,when f>0(the counterclockwise component),there are the prominent fluctuations of about 19 d periods at the 200 and 500 m levels,and there is the prominent fluctuations of about 14 d periods for clockwise component at the 800 m levels,respectively.(6) At 200,500 and 800 m levels,there are also the following prominent peaks:1) the fluctuation in the period range of about 4~6 d,which occurs in the weather process;2) the fluctuation in the period range of about 2~3 d;3) the inertial period of about 34.5 h,whose fluctuation is clockwise,and soon.(7) From the cross spectral estimates between two time series,it is shown that 1) there are significant coherence peaks for the periods of more than 15 d and 2~3 d and the diurnal and semidiurnal peaks and so on between the two time series of currents at 200 and 500 m dept hs.Bot h the current fluctuations at 200 and 500 m dept hs are synchro nous for the period of more than 15 d.2) t here ar e significant coher ence peaks for the periods of about 4~6 d,which occurs in the weather process,and 2~3 d and the diurnal and semidiurnal peaks and so on between the two time series of currents at 500 and 800 m depths.However,the phase difference of current fluctuations between two time series at 500 and 800 m levels have the time lags and forward phenomena for the above periods.
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