| Summary: | 博士 === 國立中山大學 === 海洋環境及工程學系研究所 === 107 === In the subpolar region in the southern hemisphere, the Antarctic Circumpolar Current (ACC) is one of the main sources of the Peru Current. The ACC plays an important role in the climate change of the world. The fluctuations in the ACC intensity of the western South Atlantic Ocean consequentially influence the SST (Sea Surface Temperature) and marine ecosystems. However, the variations in the SST in the Southern Ocean have rarely been addressed. It is because the South Atlantic Ocean is rarely sampled and studied tied to its inclement weather and rigorous environment in the area.
FFT, Wavelet, Empirical Orthogonal Function (EOF), Ensemble Empirical Mode Decomposition (EEMD), Harmonic analysis, Cross-Correlation Analysis (Xcorr) and low pass filter methods are applied to a 147-year (1870-2016) time series dataset of SST distributed by the Met Office Hadley Centre. We find that there are the obvious inter-annual and inter-decadal variations existing in our study area. The results show that SSTAs in the oceans west and east of the South America and Antarctic Peninsula have respectively strong positive (R = 0.56) and negative (R = −0.67) correlations with the Niño 3.4 SSTA. We further show that, statistically, the temporal variations in the SSTAs of the ACC lead the Niño 3.4 SSTA by four to six months. Such findings imply that change in the strength of El Niño-Southern Oscillation (ENSO) or circulation under the changing climate could change the climate in regions at higher latitudes as well.
EOF analyses show the particularly negative correlations (R=-0.56) with Pacific Decadal Oscillation (PDO) periods. This study further showed that changes in SSTAs in the regions mentioned above were enlarged when the PDO and the ENSO were in the same warm or cold phase, implying that changes in the SST of higher latitude oceans could be enhanced when the influence of the ENSO is considered along with the PDO. Furthermore, we analyzed the cross-correlation between the Brazil-Malvinas Confluence Zone (BMC) and PDO indexes. The result showed that the BMC index had a strong positive correlation (R=0.75) with the PDO index, when the PDO index time series led by 3 to 4 years of the BMC index time series. Such a duration was similar to the periodicity of a typical ENSO event, implying that variations in BMC index might reflect both the ENSO and PDO events.
|
|---|
