The Changing Influences of ENSO and the Pacific Meridional Mode on Mesoscale Eddies in the South China Sea
The Changing Influences of ENSO and the Pacific Meridional Mode on Mesoscale Eddies in the South China Sea
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DOI：
10.1175/jcli-d-18-0187.1
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发表时间：
2019-01
影响因子：
4.9
通讯作者：
Pengfei Tuo;Jin‐Yi Yu;Jianyu Hu
中科院分区：
文献类型：
--
作者：
Pengfei Tuo;Jin‐Yi Yu;Jianyu Hu
研究发现，厄尔尼诺-南方涛动(ENSO)与南中国海中尺度海洋涡旋活动的相关性在2004年前后发生了变化。用速度矢量法由卫星测高得到的中尺度涡旋数在2004年前与Niño-3.4指数呈显著负相关，但此后这种相关性减弱，变得不显著。进一步的分析表明，ENSO-涡旋关系受两种主要的风应力强迫机制控制：一种是与ENSO直接相关的机制，另一种是通过其副热带前兆--太平洋经向模与ENSO间接相关的机制。这两种机制都会在南海引起风应力旋度变化，从而将ENSO与南海涡旋活动联系起来。直接的ENSO机制总是通过Walker环流导致ENSO-涡负相关，而间接机制则以北部PMM(NPMM)为主，2004年前为负相关，2004年后为南方PMM(SPMM)，为正相关。结果表明，在2004年前，直接机制和间接机制相互促进，产生显著的ENSO-涡旋关系，但相互抵消，导致2004年后ENSO-涡旋关系较弱。南北PMM的相对强度是决定ENSO-涡度关系的关键，可能与太平洋年代际振荡的位相变化有关。
This study finds that the correlation between El Niño–Southern Oscillation (ENSO) and the activity of mesoscale oceanic eddies in the South China Sea (SCS) changed around 2004. The mesoscale eddy number determined from satellite altimetry observations using a geometry of the velocity vector method was significantly and negatively correlated with the Niño-3.4 index before 2004, but the correlation weakened and became insignificant afterward. Further analyses reveal that the ENSO–eddy relation is controlled by two major wind stress forcing mechanisms: one directly related to ENSO and the other indirectly related to ENSO through its subtropical precursor—the Pacific meridional modes (PMMs). Both mechanisms induce wind stress curl variations over the SCS that link ENSO to SCS eddy activities. While the direct ENSO mechanism always induces a negative ENSO–eddy correlation through the Walker circulation, the indirect mechanism is dominated by the northern PMM (nPMM), resulting in a negative ENSO–eddy correlation before 2004, and by the southern PMM (sPMM) after 2004, resulting in a positive ENSO–eddy correlation. As a result, the direct and indirect mechanisms enhance each other to produce a significant ENSO–eddy relation before 2004, but they cancel each other out, resulting in a weak ENSO–eddy relation afterward. The relative strengths of the northern and southern PMMs are the key to determining the ENSO–eddy relation and may be related to a phase change of the interdecadal Pacific oscillation.