孟加拉湾热源与中国夏季雨带分布的关系——Rossby波的作用

The relationship between bay of Bengal heating and summer monsoon precipitation over China——the effect of Rossby wave

应用水平非均匀基流下球面行星波的传播理论,分析了夏季风爆发后孟加拉湾热源产生的Rossby波的频散路径及其与中国夏季大范围雨带分布的关系。研究结果表明:10—20d周期的Rossby波从孟加拉湾往北穿过中南半岛到达我国西南地区、进一步穿过长江流域到达华北和东北地区,其传播路径与我国夏季降水逐渐北移路径非常吻合,Rossby波的能量7—10d可以频散到当月的雨带区域;而30—60d周期的Rossby波传播路径主要分为两支,一支与10—20d周期的波路径一致,另外一支从孟加拉湾东传到菲律宾附近然后转向西北太平洋、到达日本及其以东沿海,之后继续往北美洲传播,与准定常Rossby波的传播路径一致,可以解释东亚-太平洋遥相关波列,其直接影响的范围主要分布在我国东部沿海及日本一带。对影响我国夏季降水的Rossby波传播过程中能量变化特征的分析表明:夏季低层850hPa上Rossby波传播过程能量不断衰减,扰动动能向基本流动能转化,而高空200hPa上Rossby波能量以振荡为主,波流之间相互转换。

Based on the theory of planetary wave propagation in the horizontal non-uniform basic flow, the propagation of Rossby wave inspired by the heating over Bay of Bengal （BOB） and its related summer precipi-tation in China has been investigated. The results show that Rossby waves of 10—20 d period commence from BOB region, pass through Indochina Peninsula, Southwest China, and arrive in the Yangtze River Basin, and then reach further to North China. The ray path is consistent with the northward propagation of the summer monsoon rainfall over China. The wave energy could disperse to the concerned rainfall regions within 7—10 days. Rossby waves of 30—60 d period propagate in two separate branches. One is consistent with the path of 10—20 d Rossby wave, and the other one propagates eastward to the South China Sea and the Philippines, and turns northward to China＆#39;s eastern coastal areas and Japan, then reaches North America eventually. The latter path is in line with the stationary Rossby wave rays, known as the EAP/PJ wave train, and has a direct impact on China eastern coastal areas and Japan. Two periods of Rossby wave could explain the low frequency oscillation features of the summer monsoon rainfall over China. Moreover, the wave energy variation during propagation has been studied. Along the propagation pathway, the wave energy decreases at lower level （850 hPa）, implying the energy is transferred to the base flow, while oscillates at the upper level （200 hPa）, indicating the wave-current interaction there.