黑潮输送的异常及其与大尺度海气相互作用的关系

ANOMALOUS TRANSPORT OF KUROSHIO AND ITS RELATIONSHIP WITH LARGE SCALE ATMOSPHERE-SEA INTERACTION

以128.5°E为界,沿27°N,北太平洋西边界流输送可以分成呈明显负相关的东、西2段。西段(即黑潮)主要参与副热带环流(STG)和经向环流(STC);东段主要参与日本东南的反气旋式涡旋再回流。从气候态来看,西段输送在7、8月份最大,3月份次大;东段输送在6—8月份最小,其它月份比较接近;整体结果表现为全年有2个接近的极大值,分别是3、4月份和7、8月份。从年序列来看,西段输送在20世纪70年代后期有一次明显的突变;而东段在1955年突然减小,在1963年突然增大。小波分析表明,东、西两段的振荡周期都随时间变化。西段输送时间序列的20a左右周期振荡在1976年以前非常明显,9a左右周期振荡在1985年以后比较显著;东段输送的13a左右周期在1976年以前显著,1985年以后的主要振荡周期从7a逐渐减小到3a左右。奇异谱分析表明,西段输送的年代际变化占总方差的45%,年际变化占总方差的13.6%;东段输送的年代际变化占总方差的24.3%,年际变化占总方差的32.3%。黑潮输送异常和太平洋年代际振荡(PDO)及ENSO有着非常密切的关系。在年代际尺度上,一个可能的过程是,PDO超前于黑潮输送异常;异常的黑潮输送通过改变北太平洋中部的SST梯度引起的海气相互作用过程而调制ENSO的变化。在年际尺度上,黑潮输送异常滞后于PDO和ENSO变化,且呈负相关。

The North Pacific western boundary current along 27°N is divided into western and eastern sectors at 128.5°E, which are significantly negatively correlated. The western sector, Kuroshio, mainly involves the subtropical gyre (STG) and the subtropical cell (STC), and the eastern sector mainly involves the anticyclonic gyre to the southeast of Japan which quickly recirculates. From the view of climatological state, the western sector reaches a maximum transport in July and August and a sub-maximum transport in March; the eastern sector reaches a minimum transport during June to August, and the transport is approximately at similar range in other months. Thus as a whole, the current has two maximum transports, respectively in March to April, and July to August. From the annual series of transport, the western sector has an apparent regime shift in the late 1970s, and the eastern sector has an abrupt decrease in 1955 and an abrupt increase in 1963. Wavelet Analysis shows that the oscillation period of both western and eastern sectors varies with time. In the sequence of Kuroshio, periodic oscillation of about 20 years is apparent before 1976, and that of about 9 years is significant after 1985; while in the sequence of eastern sector, periodic oscillation of about 13 years is apparent before 1976 and varies from 7 years to 3 years after 1985. Singular spectrum analysis (SSA) shows that the interdecadal variation accounts for 45% of the total variance and the interannual variation accounts for 13.6% for Kuroshio transport; while the interdecadal variation accounts for 24.3% of the total variance and the interannual variation accounts for 32.3% for the eastern sector. The anomalous Kuroshio transport has a close relationship with Pacific Interdecadal Oscillation (PDO) and ENSO. On an interdecadal scale, a possible process is that PDO is ahead of the anomalous Kuroshio transport, and the anomalous Kuroshio transport modulates the variation of ENSO through atmosphere-sea interaction induced by changed gradient of SST in the central North Pacific. On an interannual scale, the anomalous Kuroshio transport lags the variations of PDO and ENSO, and is negatively correlated with them.