台湾以东海域声速剖面序列的EOF分析

EOF Analysis of Sound Speed Profiles in Sea Area East of Taiwan

利用了4 a的Argo剖面序列,通过经验正交函数（EOF）分析,得出了台湾以东海域声速垂直结构的时空变化特征。EOF拟合声速剖面的精度与选取的模态数有关,合成剖面时包含的模态数越多,精度越高;前3-6个模态反映了海区声速结构的主要变化,累积方差贡献率可达89.4%-96.6%。第1模态描述了声速在垂直方向上的同相变化,具有年周期,峰值和谷值分别出现在夏季和冬季;第2模态描述了声速在近表层与次表层和主跃层的反相变化。第1、2模态的共同作用是声速垂直结构差异的主导因素,使近表层声速的季节性变化较大,而主跃层的变化相对较小;而第3模态及更高阶的模态对声速剖面的调制作用在物理意义上并不明显。

Based on the 4 years＇ Argo data,the characteristics of temporal and spatial variations in sound speed profiles（SSPs） are acquired from the sea area east of Taiwan by means of empirical orthogonal functions（EOF） method.The accuracy of the sound speed profiles fitted by means of EOF method depends upon the selected EOF modes in the fitting.The more modes are involved in the profile fitting,the better the accuracy of the fitted profile becomes.The main features of the sound speed structures in the studied area can be reflected using the first 3-6 modes.The total variance added up from the modes can be ashighas 89.4%-96.6%.The first mode denotes the variations from the surface layer to the bottom layer being in phase with each other,they are seasonal variation with the highest sound speed in summer and the lowest in winter.The second mode denotes the voriations in both the surface layer and the subsurface layer being of opposite phase to the variation in the thermoclines.Mode 1 and Mode 2 are the dominant components for expression the variant patterns in the sound speed structures,the significant seasonal variation in the top layer,and the less significant seasonal variation in the thermoclines.The third mode and the others are insignificant for reflecting the patterns in the sound speed profiles.