The Variability of Winter Monsoon Intensity in Xisha Waters, South China Sea for the Last More Than 50 Years
PENG Zicheng1,2, CHEN Tegu3, NIE Baofu3, LIU Guijian1, HE Jianfeng1, CHENG Jiman1(1. The School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China; 2. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, CAS, Xi'an 710075, China; 3. South China Sea Institute of Oceanography, CAS, Guangzhou 510301, China)
We have used correlative analysis between 1958-1997 mean December-January- February NE winter monsoon velocities, measured at the Yongxing Island Observatory, as a winter monsoon intensity index (WMI) and mean δ18O data for corresponding months from Porites lutea coral, collected in the northern part of the South China Sea, to obtain a linear equation: WMI (m/s) = -4.913-2.138δ18O (‰), r = 0.83, n = 40. The high correlative coefficient between the above-mentioned two series of WMI and δ18O data is made by using high-pass filtering method. On the basis of the calculated WMI sequence from 1944 to 1977, the interdecadal variability shows that the WMI series decreases in the 1940s-1960s, slightly increases in the 1970s, but decreases again in the 1980s-1990s. The interannual variability reveals that the WMI series decreases obviously from 1944 to 1977 with the correlative equation of WMI (m/s) = 79.69-0.0377 Year, r = 0.68, n = 54. The linear slope is negative, which means that the WMI series decreases by about 0.4 m/s every 10 years. The power-spectral analysis displays that a 54-year WMI series is provided with periodicity of a 2.5-7 year band, which is related to the QBO band of 2-2.4 years and ENSO band of 3-8 years. Therefore, it can be considered that the winter monsoon variability in the South China Sea is also controlled by the global change.