台风螺旋雨带——涡旋Rossby波

THE SPIRAL RAIN BANDS OF TROPICAL CYCLONE AND VORTEX ROSSBY WAVES

台风中的螺旋云雨带是由多种探测手段被观测到的现象 ,是为大家所共识的不争事实。但是 ,对它的形成、维持的理论解释 ,虽有多种学说 ,一直以来人们都倾向于重力惯性波说。而重力惯性波说有一个致命的弱点 ,即波的相速理论值为 10 1m/s量级 ,它要比螺旋云雨带实测移速只有 10 0 m/s几乎大一个量级。于是从前几年开始 ,人们又回到 30多年前提出的涡旋 Rossby波说那里去寻找合适的解释。经典的Rossby波是 β =(df/dy)作用的大尺度波动 ,而适用于台风中螺旋云雨带的涡旋———Rossby波乃是 f平面 (β =0 )上的中尺度波动。那末 ,对这两类尺度不同和成波机理不同的波动 ,何以均冠予Rossby波一词 ?本文试图从动力学等价原理上 ,对此作统一联系的说明。其结果是 :台风基本气流的涡度 ζ随径向 (r)变化的梯度d ζdr=1rr(r vλ) ,在动力学上等价于科氏参数 f随纬度变化的梯度即β=df/dy ;或者说它们在绝对涡度守恒的前提下 。

The spiral rain bands of tropical cyclone and the vortex Rossby waves are reviewed. It is pointed specially that the axisymmetrizing disturbances on a vortexare accompanied by outward-propagating vortex Rossby waves whose restoring mechanism is associated with the gradient of storm vorticity, for the goal of elucidating the dynamics of outward-propagating spiral bands in tropical cyclone. The theoritical value of its outward-propagating speed is about O(10°m/s),almost to be consistent with observational one of spiral rain bands. Based on the principle of conservation of vorticity (or PV), the restoring mechanism of vortex Rossby wave is equivalent dynamically to the planetary Rossby wave.