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梁钊明, 王东海. 一次台风变性并入东北冷涡过程的动力诊断分析[J]. 大气科学, 2015, 39(2): 397-412. DOI: 10.3878/j.issn.1006-9895.1407.14128
引用本文: 梁钊明, 王东海. 一次台风变性并入东北冷涡过程的动力诊断分析[J]. 大气科学, 2015, 39(2): 397-412. DOI: 10.3878/j.issn.1006-9895.1407.14128
LIANG Zhaoming, WANG Donghai. A Diagnostic Study of a Typhoon Transitioning and Merging into the Northeast Cold Vortex[J]. Chinese Journal of Atmospheric Sciences, 2015, 39(2): 397-412. DOI: 10.3878/j.issn.1006-9895.1407.14128
Citation: LIANG Zhaoming, WANG Donghai. A Diagnostic Study of a Typhoon Transitioning and Merging into the Northeast Cold Vortex[J]. Chinese Journal of Atmospheric Sciences, 2015, 39(2): 397-412. DOI: 10.3878/j.issn.1006-9895.1407.14128

一次台风变性并入东北冷涡过程的动力诊断分析

A Diagnostic Study of a Typhoon Transitioning and Merging into the Northeast Cold Vortex

  • 摘要: 台风北移变性并入东北冷涡是造成东北地区夏季大范围暴雨的主要形式之一, 但其中的热动力结构变化特征及其物理机制尚不清晰。本文利用美国国家环境预报中心(NCEP)的再分析资料对一次台风变性并入东北冷涡过程进行动力诊断分析, 分析结果显示:冷涡冷空气的不断侵入以及台风移动形成的相对冷平流使得台风暖心结构消亡, 其低层低压辐合和高层高压辐散结构消失, 变性并入东北冷涡后气旋整层偏冷, 低层出现冷中心。台风变性并入东北冷涡过程中, 冷涡中心附近高空急流南侧的反气旋切变抑制气旋直接往高空发展, 而急流轴左侧的热动力分布特征有利于垂直涡度的发展, 变性后的气旋环流向冷涡的移近有利于急流轴维持倾斜, 从而促进气旋向高空冷涡倾斜发展。同时, 冷空气在气旋低层附近堆积导致等假相当位温线发生倾斜, 造成垂直涡度在气旋中层倾斜发展。台风变性并入东北冷涡后, 高空冷涡槽底的正垂直涡度平流促进气旋由中层直接向高层发展, 而高空冷涡槽底急流促进正垂直涡度平流的维持。气旋高空环流的发展反过来削弱了东北冷涡的高层环流, 导致高空冷涡中心出现北撤。

     

    Abstract: A typhoon transitioning to an extratropical cyclone and merging into the Northeast cold vortex is one of the main weather processes causing widespread heavy rainfall in northeastern China in summer.However, the evolution characteristics and mechanism of the thermal and dynamical structures of the typhoon and the Northeast cold vortex in this type of process are not well understood.This study applies the re-analysis data of the National Centers for Environmental Prediction (NCEP) to diagnose an event in which a typhoon transitions and merges into the Northeast cold vortex.The results show that the persistent cold air invasion from the Northeast cold vortex and the relative cold advection caused by the movement of the typhoon gradually destroyed the warm core of the typhoon.As a result, the low-level low-pressure convergence and upper-level high-pressure divergence associated with the warm core disappeared.After the typhoon transitioned and merged into the Northeast cold vortex, the entire troposphere became relatively cold, and a cold center formed at the low troposphere.As the typhoon transitioned to an extratropical cyclone and merged intothe Northeast cold vortex, the anti-cyclonic wind shear at the south side of the upper-level jet near the center of the Northeast cold vortex inhibited the vertical upward development of the cyclone.However, the features of thermal and dynamical distributions on the left side of the upper-level jet axis favored vertical vorticity development, and the maintenance of the tilted upper-level jet axis caused by the cyclone approaching the Northeast cold vortex enhanced the slantwise upward development of the cyclone.Moreover, the vertical vorticity at the middle troposphere of the cyclone increased rapidly due to the slantwise lifting of low-level air along the tilting pseudo-equivalent potential temperature isolines from the east side of the cyclone.The tilting of pseudo-equivalent potential temperature isolines were caused by the cold air packing near the low levels of the cyclone.After the typhoon transitioned and merged into the Northeast cold vortex, a distinct positive vertical vorticity advection from the upper-level cold vortex bottom prompted the vertical upward development of the cyclone.The eastward movement of the jet at the upper-level cold vortex bottom was favorable for maintaining the positive vertical vorticity advection.The vertically upward development of the cyclonic circulation weakened the upper-level circulation of the Northeast cold vortex, leading to its northward retreat.

     

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