摘要: |
近海迅速增强(RI)是当前台风强度预报中的难点。为加深台风强度变化机理认识和提高台风强度预报水平,利用中国气象局最佳路径数据和 ERA5 大气再分析资料,分析了历史罕见的东海近海台风“黑格比”(2020)在RI阶段的高层环境场特征,着重探讨了高层环境场影响台风强度的可能过程。结果显示:(1)“黑格比”的RI过程中,南亚高压与热带对流层上部槽之间的强风速带增强了台风东南侧高空外流,中纬度高空槽增强了台风北侧高空外流。(2) 高层环境场与台风高空外流的相互作用有利于台风增强。一方面,有利的高空形势向台风中心传播涡动角动量通量辐合来增强台风高空外流,进而加强高空外流与上升运动形成的次级环流,促进台风中心气压降低和强度增强;另一方面,增强的台风高空外流限制了垂直风切变的发展,从而减弱环境场的通风效应,有助于台风加强。(3) 360 K等熵面上环境场高位涡向台风中心输送,同时平流层“高位涡库”向下打通,可以促进台风高层暖心形成,有利于台风加强。针对高层环境场的综合分析可以为台风强度预报提供一定的参考。 |
关键词: 台风 迅速增强 高层环境场 高空外流 垂直风切变 位涡 |
DOI:10.16032/j.issn.1004-4965.2024.073 |
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Impact of Upper-tropospheric Environmental Field on Rapid Intensification of Typhoon Hagupit (2020) |
JIN Ru, DONG Meiying, LI Ying, WANG Ning
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Zhejiang Institute of Meteorological Sciences/Zhejiang Branch, Chinese Academy of Meteorological Sciences, Hangzhou 310008, China
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Abstract: |
Rapid intensification (RI) remains a challenge in typhoon intensity forecasting. In order to enhance the understanding of the mechanism behind typhoon intensity variation and to improve the accuracy of typhoon intensity forecasts, this study analyzed the characteristics of the upper-tropospheric environmental field during the RI of Typhoon Hagupit (2020). Using the CMA Tropical Cyclone Best Track Dataset and the ERA5 reanalysis data, the present study discussed the possible mechanisms by which the upper-tropospheric environmental field affected typhoon intensity. The results show that: (1) The upper-level weather systems affecting the intensity of Typhoon Hagupit (2020) mainly included the South Asian high, the tropical upper-tropospheric trough, and the mid-latitude trough. (2) The upper-tropospheric environmental field facilitated the intensification of Typhoon Hagupit (2020) through its interaction with the upper-level outflow of the typhoon. On the one hand, favorable upper-tropospheric circulation enhanced the upper-level outflow by directing the eddy flux convergence of relative angular momentum to propagate toward the typhoon center. This process promoted the secondary circulation formed by the outflow and upward motion, leading to a decrease in the central pressure of Typhoon Hagupit (2020) and an increase in its intensity. On the other hand, the enhanced outflow restricted the development of the vertical wind shear and, consequently, weakened the ventilation effect and intensified the typhoon. (3) On the 360-K isentropic surface, the presence of small-scale positive potential vorticity (PV) anomalies atop the typhoon circulation enhanced the typhoon’s intensity. At the same time, the“high-PV pool”in the stratosphere was connected with the positive PV anomaly region in the middle troposphere, which could promote the formation of the upper-level warm core and intensify the typhoon. The present study shows that a comprehensive analysis of the upper-tropospheric environmental field can offer insights for typhoon intensity forecasting. |
Key words: typhoon rapid intensification upper-tropospheric environmental field upper-level outflow vertical wind shear potential vorticity |