The Looping Motion and the Asymmetry of Tropical Cyclone

[摘要] We study the looping motion of tropical cyclone by a numerical simulation for the case of no steering current in order to investigate the relation between the asymmetry and the motion of model vortex. The dynamically balanced vortex is used initially to avoid an initial unrealistic motion of the vortex.The mean winds in each pressure level rotate counterclockwise in the developing stage in both f-and β-plane cases. As the mean wind is produced by the asymmetric distribution of winds, the rotation of the mean wind is considered as an inertial wave propagating on the eyewall. We apply the linear wave theory to a modified Rankine vortex which has an internal boundary in no gravity field. The angular velocity of this inertial wave is estimated approximately at a half of the vorticity in the outer region of the eyewall.If the distribution of azimuthal wind is in proportion to 1/r approximately, the looping motion will be absent as the vorticity becomes zero in the outer area of the eyewall. The looping motion is commonly cyclonic, because the vorticity near the eyewall is positive due to the surface friction and the lateral mixing of momentum.

[学科分类] 大气科学