Quantifying the Contribution of Track Changes to Interannual Variations of North Atlantic Intense Hurricanes

Abstract

Previous studies have linked interannual variability of tropical cyclone (TC) intensity in the North Atlantic basin (NA) to Sahelian rainfall, vertical shear of the environmental flow, and relative sea surface temperature (SST). In this study, the contribution of TC track changes to the interannual variations of intense hurricane activity in the North Atlantic basin is evaluated through numerical experiments. It is found that that observed interannual variations of the frequency of intense hurricanes during the period 1958–2017 are dynamically consistent with changes in the large-scale ocean/atmosphere environment.

Track changes can account for ∼50% of the interannual variability of intense hurricanes, while no significant difference is found for individual environmental parameters between active and inactive years. The only significant difference between active and inactive years is in the duration of TC intensification in the region east of 60°W. The duration increase is not due to the slow-down of TC translation. In active years, a southeastward shift of the formation location in the region east of 60°W causes TCs to take a westward prevailing track, which allows TCs to have a longer opportunity for intensification. On the other hand, most TCs in inactive years take a recurving track, leading to a shorter duration of intensification. This study suggests that the influence of track changes should be considered to understand the basin-wide intensity changes in the North Atlantic basin on the interannual time scale.

摘 要

一般认为北大西洋热带气旋强度的年际变化与非洲萨赫勒地区降水量、海区环境风的垂直切变和相对海表面温度变化有关。本研究通过数值试验定量评估了飓风路径变化对北大西洋4、5级飓风活动年际变化的贡献, 首先验证了1958-2017年期间强飓风频数年际变化与大尺度海洋/大气环境的变化动力学上的一致性, 然后分别评估各个大尺度环境因子和热带气旋路径变化的贡献。模拟结果表明, 仅仅环境参数引起的强飓风年际变化并不明显, 而热带气旋路径的变化对强飓风活动年际变化有重要影响。路径的变化主要来自生成位置的变化, 在西经60度以东地区, 热带气旋生成位置的变化造成了盛行路径的变化, 进而影响了飓风的强度。在活跃年份, 热带气旋生成位置向东南偏移, 使得盛行路径偏西, 从而有了更多的增强时间; 在不活跃的年份, 热带气旋盛行远海转向的路径, 增强时间相对较短。这项研究表明, 热带气旋路径变化是影响海盆尺度热带气旋强度的一个重要因子。