辐散风作用下低频Rossby波的能量传播

PROPAGATION OF LOW FREQUENCY ROSSBY WAVE WITH DIVERGENT WIND

文中研究了热力强迫所激发的辐散风对低频Rossby波能量传播的影响 ,推导出辐散风作用下的Rossby波的频散关系和群速度表达式。理论分析表明 :如果扰动流函数与速度势的位相差α∈ (0 ,π) ,那么辐散风将减小Ross by波的圆频率 ,增大群速度的纬向分量 ,加速Rossby波在纬向方向上的传播 ;辐散风对经向群速度的影响是比较复杂的。波射线的分析表明 ,在纬向基本气流为常数的情况下 ,辐散风作用下的低频Rossby波从初始位置到反射纬度的传播路径表现为一段光滑的大弧 ;对于周期为 30d、纬向波数k =3,4的Rossby波 ,当辐散风减弱时 ,波能量经向传播距离和纬向传播距离都增大。对于k =3的Rossby波 ,当辐散风减弱时 ,Rossby波的经向传播范围增大 ,但振幅强度减小。

The effect of divergent wind excited by external thermal forcing on propagation of low frequency Rossby wave is investigated in a barotropic atmosphere. The dispersion relation and group velocity expression of low-frequency Rossby wave with divergent wind are derived. Theoretical analysis shows that for α ∈(0,π) where α is phase difference between stream function and velocity potential, divergent wind may reduce frequency of Rossby wave and increase zonal group velocity. The modification to meridional group velocity made by divergent wind is much more complicated than that to zonal group velocity. Rossby wave ray analysis indicates that for the constant zonal basic flow, the path along which Rossby wave with divergent wind propagates from initial location to reflection latitude is regarded as a piece of smooth arc. For 30-day period, the zonal and meridional propagation distances of Rossby waves with k =3,4 will lengthen when divergent wind weaken. The calculation of Rossby wave amplitude reveals that for weakened divergent wind, the meridional range in which Rossby wave with k =3 is propagable is extended and the amplitude decreases.