东亚经向波列对中国中东部盛夏气温的影响

The Impact of Meridional Wave Trains over East Asia on the Air Temperature over Central and East China in Midsummer Time

利用1980-2008年CN05月平均地面气温格点资料和NCEP/NCAR再分析资料,首先分析了中国中东部7月地面平均气温的变化特征,得到3个主要模态,其方差贡献率分别为44%、17%、11%,其中第1模态显示了江淮、华北和东北地区近30年来地面平均气温的线性升高趋势;第2模态显示了江淮-江南地区与东北东部地区的"偶极子"型反位相分布特征,第3模态显示了华北-黄淮地区与华南和东北地区的"三极子"型分布特征。由于前人已对第1模态做了详细讨论,本文主要分析第2和第3模态。分析结果显示,东亚经向波列对"偶极子"型和"三极子"型有以下重要影响:当东亚西太平洋地区的经向波列整体偏北时,易出现第2模态的"偶极子"型特征,当该波列整体偏南时,有利于出现第3模态的"三极子"型特征;当中国华南沿海、台湾地区附近对流活动偏弱时,有利于对应第2模态的负位相的经向波列出现,反之亦然。在关于第2模态正负异常年的合成场中,850 h Pa上东亚沿海的波作用通量在低纬度地区主要是向北传播的,而300 h Pa上波作用通量在低纬度以北传为主,中纬度以东传为主,但低纬度的对流加热异常情况及北传的波作用通量对于第3模态不明显。

Based on the CN05 grid datasets of monthly mean surface air temperature from 1980 to 2008,the distribution of surface air temperature over Central and East China in July is studied,and three main modes are obtained,the three leading modes explained 44%,17% and 11% of the total variance,respectively. The first mode shows a linear trend of surface air temperature over Jianghuai area in the North China and Northeast China in the last thirty years,the second mode shows a ‘dipole＇pattern between Jianghuai-Jiangnan area and the east portion of Northeast China,and the third mode shows a ‘tripole＇pattern between Huabei-Huanghuai area,the South China and the Northeast China. Because of the characteristics of the first mode have been discussed in a number of articles,the second and third modes account for the main component. The composite fields indicate that the meridional wave trains over East Asia play an important role on the second and third modes： When the meridional wave trains over East Asia and Western Pacific locate north,it＇s in favor of generating the above dipole pattern. When the wave trains locate south,it＇s in favor of generating the above tripole pattern. When the convective activities over South China and Taiwan Island is weaker than normal,it＇s favorable to generate the negative phase of the meridional wave trains corresponding to the second mode,and vice versa. In the composite fields of positive and negative years about the second mode,wave activity flux mainly point to north at lowlatitudes at the 850 h Pa level near East Asian coast. At 300 h Pa level,wave activity flux mainly point to north at lowlatitudes and point to east at middle latitudes. However,OLR and wave activity flux anamolies at lowlatitudes in the third mode are not significant.