东亚夏季风强弱年季节内振荡的传播特征

The propagating characteristics of intraseasonal oscillation in strong and weak east Asian summer monsoon years

利用1979—2007年的逐日OLR资料和1960—2007年NCEP/NCAR逐日再分析风场资料,采用合成分析和波谱分析方法研究了强弱夏季风年北半球夏季季节内振荡(BSISO)的基本特征。结果表明:BSISO的能谱主要分布在1波和2波范围内,在热带地区,主要是以1波东传为主,在较高纬度,可以看到明显的西传分量;而在经向上主要是以30～60 d周期的北传为主。在强(弱)夏季风年时,纬向方向上,热带地区ISO东传加强(减弱),而20°N以北的较高纬度,ISO西传是减弱(加强)的;经向方向上,最显著的差异是西太平洋地区北传ISO是加强(减弱)的。造成强弱夏季风年ISO传播差异的原因是由于强弱夏季风年中西太平洋地区纬向风场和对流场存在明显差异,在这种大范围大气环流异常的情况下,ISO的经向和纬向传播产生了明显的差异。

Based on the 1979—2007 daily mean outgoing longwave radiation and 1960—2007 NCEP/NCAR daily reanalysis wind field,the composite analysis and wavenumber-frequency analysis are applied to the characteristics of the strong and weak summer monsoon years in the boreal summer intraseasonal oscillation（BSISO）.It is shown that the BSISO energy spectrum is mainly distributed in the wavenumber-1 and wavenumber-2.In the tropics,BSISO mainly propagates eastward in the form of wavenumber-1,and in the higher latitudes,the westward propagation is clear;in the meridional direction it is the northward propagation of 30-60 d periods.In the strong（weak） summer monsoon years in the zonal direction the eastward propagation is enhanced（weakened） in the tropical region,whereas in the higher latitude of the north of 20 °N westward propagating ISO is weakened（strengthened）;in the meridional direction the most significant difference is that the northward propagating ISO is strengthened（weakened） over the western Pacific.It is the difference of the propagating ISO in strong and weak summer monsoon years that may lead to the difference of the zonal wind field and convection in western and central Pacific,the propagating ISO causes an apparent difference in this large-scale atmospheric circulation anomalies.