Summertime Subtropical Stationary Waves in the Northern Hemisphere: Variability, Forcing Mechanisms, and Impacts on Tropical Cyclone Activity
Summertime Subtropical Stationary Waves in the Northern Hemisphere: Variability, Forcing Mechanisms, and Impacts on Tropical Cyclone Activity
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DOI：
10.1175/jcli-d-22-0233.1
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发表时间：
2022-10
影响因子：
4.9
通讯作者：
Chuan‐Chieh Chang;Zhuo Wang-;M. Ting;Zhao Ming
中科院分区：
文献类型：
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作者：
Chuan‐Chieh Chang;Zhuo Wang-;M. Ting;Zhao Ming
本文研究了夏季副热带驻波的年际变率、强迫机制及其与区域热带气旋变率的关系。确定了表征副热带平稳波年际变化的两个指标：纬向波数-1分量（WN1）的纵向位移和纬向波数-2分量（WN2）的强度变化。这两个指数具有较强的反相关关系，为描述副热带驻波的年际变化提供了简单的指标。此外，WN1的纵向位移与北太平洋和北大西洋上空TC活动的变率显著相关，其对区域TC活动的影响可以通过垂直风切变、对流层湿度和罗斯比波破碎频率的变化来解释。副热带驻波与不同海洋区域的降水异常密切相关，暗示低频气候模式可能对降水异常产生影响。利用社区地球系统模式第2版（CESM2）进行的半理想化实验表明，WN1的经度受到ENSO的强烈调制，大西洋主发展区和北太平洋中部的海温异常也受到ENSO的强烈调制。利用斜压平稳波模式进一步诊断表明，非绝热加热在驱动平稳波年际变化中起主导作用，并证实了不同海气耦合模式对副热带平稳波的影响。总的来说，副热带静止波为理解ENSO、大西洋经向模态和温带罗斯比波破碎等各种强迫因子对北大西洋和北太平洋TC活动的影响提供了一个统一的框架。
The interannual variability of summertime subtropical stationary waves, the forcing mechanisms, and their connections to regional tropical cyclone (TC) variability are investigated in this study. Two indices are identified to characterize the interannual variability of subtropical stationary waves: the longitudinal displacement of the zonal wavenumber-1 component (WN1) and the intensity change of the zonal wavenumber-2 component (WN2). These two indices are strongly anticorrelated and offer simple metrics to depict the interannual variability of subtropical stationary waves. Furthermore, the longitudinal displacement of the WN1 is significantly correlated with the variability of TC activity over the North Pacific and North Atlantic, and its influences on regional TC activity can be explained by variations in vertical wind shear, tropospheric humidity, and the frequency of Rossby wave breaking. The subtropical stationary waves are strongly related to precipitation anomalies over different oceanic regions, implying the possible impacts of low-frequency climate modes. A semi-idealized experiments using the Community Earth System Model version 2 (CESM2) show that the longitude of the WN1 is strongly modulated by ENSO, as well as SST anomalies over the Atlantic main development region and the central North Pacific. Further diagnosis using a baroclinic stationary wave model demonstrates the dominant role of diabatic heating in driving the interannual variability of stationary waves and confirms the impacts of different air-sea coupled modes on subtropical stationary waves. Overall, subtropical stationary waves provide a unified framework to understand the impacts of various forcing agents, such as ENSO, Atlantic meridional mode, and extratropical Rossby wave breaking, on TC activity over the North Atlantic and North Pacific.