Alignment of Track Oscillations during Tropical Cyclone Rapid Intensification

Abstract

Recent studies on tropical cyclone (TC) intensity change indicate that the development of a vertically aligned TC circulation is a key feature of its rapid intensification (RI), however, understanding how vortex alignment occurs remains a challenging topic in TC intensity change research. Based on the simulation outputs of North Atlantic Hurricane Wilma (2005) and western North Pacific Typhoon Rammasun (2014), vortex track oscillations at different vertical levels and their associated role in vortex alignment are examined to improve our understanding of the vortex alignment during RI of TCs with initial hurricane intensity. It is found that vortex tracks at different vertical levels oscillate consistently in speed and direction during the RI of the two simulated TCs. While the consistent track oscillation reduces the oscillation tilt during RI, the reduction of vortex tilt results mainly from the mean track before RI. It is also found that the vortex tilt is primarily due to the mean vortex track before and after RI. The track oscillations are closely associated with wavenumber-1 vortex Rossby waves that are dominant wavenumber-1 circulations in the TC inner-core region. This study suggests that the dynamics of the wavenumber-1 vortex Rossby waves play an important role in the regulation of the physical processes associated with the track oscillation and vertical alignment of TCs.

摘要

近年来对热带气旋的强度变化研究表明, 热带气旋环流的垂直排列发展是其发生快速增强过程的一个关键特征, 但是理解涡旋垂直排列的发生过程仍然是热带气旋强度变化研究中的一个难题. 本文基于北大西洋飓风威尔玛(2005)和西北太平洋台风威马逊(2014)的模拟输出, 研究了涡旋不同垂直层次上的路径振荡以及其对于涡旋垂直排列的相关作用, 以提高我们对于具有初始飓风强度的热带气旋在快速增强期间涡旋垂直排列的认识. 研究结果表明, 在两个模拟的热带气旋的快速增强过程中, 不同垂直高度上涡旋的路径振荡在速度和方向上维持一致. 在快速增强期间, 涡旋高低层一致的路径振荡减小了振荡倾斜程度, 同时发现涡旋倾斜主要由快速增强前后的涡旋平均路径导致. 涡旋的路径振荡与热带气旋内核区域占主导地位的一波涡旋罗斯贝波密切相关. 研究表明, 一波涡旋罗斯贝波动力学与热带气旋路径振荡和在与涡旋垂直排列相关的物理中起着重要的调节作用.