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大气涡旋速度场和螺旋形成机理

Spiral Structures in Atmospheric Vortices: Velocity Fields and Formation Mechanisms

  • 摘要: 基于力的平衡原理,本文利用柱坐标系(r, θ, z)的Navier-Stokes方程,求出了大气中纬度气旋,台风和龙卷风,三维螺旋涡旋速度场。并由此求出三维速度均为零的奇点(临界点或平衡态),它们均是鞍焦点。中纬度气旋有两个奇点:一个在地面,另一个在对流层顶。龙卷风仅有一个奇点:在超级暴雨云底部。台风也有两个奇点,一个在地表眼壁处,另一个在地表台风眼中心。由速度场求出了水平散度D和垂直涡度ωz及涡旋形状曲面,它们均和实际观测相吻合。三种螺旋涡旋的形成机理不同,中纬度气旋是由于地表摩擦力穿过等压线所引起的水平辐合,龙卷风是由于暴雨云底强烈的水平辐合引起的涡管伸长,台风是由于海洋整体积云带的上升运动,辐散辐合随高度不变。

     

    Abstract: Based on the principle of force equilibrium, this paper employs the Navier-Stokes equations in cylindrical coordinates (r, θ, z)to derive the three-dimensional spiral vortex velocity fields of mid-latitude cyclones, typhoons, and tornadoes. Singular points (critical points or equilibrium states) where the three-dimensional velocity of the aforementioned three types of vortices is zero are determined, all of which are saddle-focus points. Mid-latitude cyclones feature two singular points: one at the surface and the other at the top of the troposphere. Tornadoes have a single singular point at the base of the supercell storm cloud. Typhoons also exhibits two singular points, one located at the eyewall surface and the other at the center of the eyewall on the surface. And from the velocity field, the horizontal divergence (D), vertical vorticity (ωz), and the vortex shape surface are obtained, which are consistent with observational data. We found that the formation mechanisms of the three spiral vortices are different. Specifically, mid-latitude cyclones are caused by horizontal convergence due to surface friction crossing isobars, tornadoes are caused by vortex tube stretching due to strong horizontal convergence at the bottom of storm clouds, and typhoons are caused by the rising motion of the whole cumulus cloud belt over the ocean, with divergence and convergence unchanged with height.

     

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