亚太季风各子系统的准两年变化特征及其比较

FEATURES AND COMPARISONS OF THE QUASI-BIENNIAL VARIATIONS IN THE ASIAN-PACIFIC MONSOON SUBSYSTEMS

亚太季风各子系统(南亚季风、南海季风、西北太平洋季风和东亚副热带季风)都具有显著的准两年变化周期,利用4个季风指数研究它们准两年模态振幅的演变和相关的环流变化。结果表明,亚太季风各子系统的准两年模态有明显的年代际变化,并不是一直有效地影响季风区。与亚太季风各子系统准两年变化相关的海温异常,低层风场也有不同的分布特点和演变特征。

TBO is a strong quasi-periodic phenomenon on large scale in the troposphere, only weaker than EI Nifio-Southern Oscillation（ENSO）. Together with ENSO, TBO affects the atmospheric circulation and leads to weather and climate anomalies. The National Centers for Environmental Prediction（NCEP） reanalysis data, Climate Diagnostics Center Merged Analysis of Precipitation（CMAP） precipitation and NOAA Extended Reconstructed Sea Surface Temperature（SST） have been used in this paper to study the quasi-biennial variations in Asian-Pacific monsoon subsystems and associated SST anomalies（SSTA） and wind anomalies. Four monsoon indices are computed from NCEP/NCAR reanalysis to represent the South Asian monsoon （SAM）, South China Sea summer monsoon（SCSSM）, western North Pacific monsoon（WNPM） and East Asian subtropical monsoon（EAM）, respectively. The quasi-biennial periods are very significant in Asian-Pacific monsoon through power spectrum analysis. For SAM and EAM, with moderate effects by ENSO, the quasi-biennial periods are most important. For SCSSM and WNPM, due to the effect of ENSO, the quasi-biennial periods are of secondary periods. There are obvious interdecadal variations in the quasi-biennial modes of Asian-Pacific monsoon. So in the negative phase the biennial modes will not be significant or outstanding. The wind anomalies and SSTA associated with the biennial modes are very different in the SAM, WNPM and EAM regions. Since the WNPM and SCSSM are very similar in the biennial modes, they can be combined into one subsystem, called SCS/WNPM.