台风麦莎的正压特征波动结构及其稳定性

Barotropic eigenvalue wave structure and stability of Typhoon Matsa

利用中尺度WRF模式对2005年8月西北太平洋台风麦莎(Matsa)进行了精细的数值模拟。使用模式输出资料,对正压浅水方程组进行了数值差分计算,分析它在最大强度时刻的正压特征波动结构和稳定性。结果表明,台风麦莎内部包含有沿逆时针方向传播的重力惯性外波和涡旋Ross-by波,两种波动的结构和稳定性存在显著性差异。前者主要存在于台风外围,增长率随波长的减小而增加,台风外围的波动相速度为48.9～68.5m/s;后者主要位于距离台风中心200km内,表现为3波最不稳定,半径100km处相速度约为5m/s。此外,重力惯性外波的扰动风场与高度场基本相垂直,扰动散涡比值大于3倍,甚至达到103倍,运动以辐合、辐散为主;涡旋Rossby波的扰动风场基本平行于高度场,扰动散涡比值为10-1～10-2,涡旋运动是其主要运动,与内螺旋雨带沿着切向圆周方向的传播具有密切关系。

The masoscale WRF model is used to simulate Typhoon Matsa that occurred over the western North Pacific in August 2005. The simulation data are applied to a barotropic shallow water equation to study the barotropic characteristic wave structures and their stabilities when Matsa reaches its peak. The results show that there are counterclockwise-propagating external inertial-gravity waves and vortex Rossby waves inside Matsa, which have different structures and stabilities. The external inertial-gravity waves occur the outer part of Matsa, and their growth rate increases as wavelength reduces, and the wave phase speed over the outer part is 48.9-68.5 m·s^-1. The Rossby waves appear over the 200 km of center area,and their wave number-3 is the most unstable,with 5 m·s^-1 phase speed at the 100 km radius. In addition, the perturbation wind fields of the external inertial-gravity waves are generally perpendicular to the height fields, and the ratio of perturbed divergence to perturbed vorticity is over 3 and could be up to 10^3, indicating that the waves are associated with divergence. The perturbed wind fields of the Rossby waves are generally parallel to the height fields, the ratio of perturbed divergence to perturbed vorticity is 10^-1-10^-2, and the waves are related to vorticity, which is intimately associated with tangential propagation of spiral rainbands.