Kinetic Energy Budgets during the Rapid Intensification of Typhoon Rammasun (2014)

Abstract

In this study, Typhoon Rammasun (2014) was simulated using the Weather Research and Forecasting model to examine the kinetic energy during rapid intensification (RI). Budget analyses revealed that in the inner area of the typhoon, the conversion from symmetric divergent kinetic energy associated with the collocation of strong cyclonic circulation and inward flow led to an increase in the symmetric rotational kinetic energy in the lower troposphere. The increase in the symmetric rotational kinetic energy in the mid and upper troposphere resulted from the upward transport of symmetric rotational kinetic energy from the lower troposphere. In the outer area, both typhoon and Earth’s rotation played equally important roles in the conversion from symmetric divergent kinetic energy to symmetric rotational kinetic energy in the lower troposphere. The decrease in the symmetric rotational kinetic energy in the upper troposphere was caused by the conversion to asymmetric rotational kinetic energy through the collocation of symmetric tangential rotational winds and the radial advection of asymmetric tangential rotational winds by radial environmental winds.

摘 要

以往对于热带气旋快速增强机制的研究通常集中在最大风速所在的内核区域进行. 本研究对 2014 年的台风个例威马逊进行了分析, 除内核区域外, 还分析了台风外部区域快速增强期间的动能收支. 对低层旋转动能收支的分析显示, 在台风内区, 气旋式切向风和向内的辐散流相互作用造成的对称辐散动能向对称旋转动能的转换导致了对流层低层对称旋转动能的增加. 对流层中高层对称旋转动能的增加是由于对称旋转动能从对流层低层向中高层输送引起的. 在台风外区, 台风和地球自转在对流层低层的对称辐散动能向对称旋转动能的转换中发挥了同样重要的作用. 对流层高层对称旋转动能的减弱是通过对称切向旋转风和径向环境风对非对称切向旋转风的径向平流的相互作用引起的低层旋转动能向非对称旋转动能的转换所致. 本研究的结果表明, 低层入流在快速增强期间发挥了以下重要作用: 低层入流与向外位势梯度方向相反, 向外位势梯度将可将位能转换为对称辐散动能; 低层入流与气旋切向流相互作用, 将对称辐散动能转换为对称旋转动能; 低空入流导致台风内区向上运动, 将动能从对流层低层输送到对流层中高层.