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长、短东移路径暖季高影响高原涡动力结构特征的对比分析

Comparative Analysis of Dynamic Structural Characteristics of High-Impact Eastward-Moving Tibetan Plateau Vortices with Long and Short Paths in the Warm Season

  • 摘要: 利用1998~2018年5~9月NCEP/NCAR全球分析数据、大气观测资料、青藏高原低涡切变线年鉴,采用伴随低涡活动的动态合成方法比较分析了准平直东移长、短路径暖季高影响高原涡的结构特征,进一步讨论了长、短路径涡的强度与其结构的关系,从而说明长、短路径涡的演变某种程度上是由低涡自身的结构决定的。其主要结论如下:(1)长、短路径涡相同的结构特征有:生成时是浅薄的天气系统、移出高原后发展为较深厚的天气系统;在不同的活动阶段低涡的涡度变化趋势一致。(2)长、短路径涡的结构特征明显差别表现在:加强时,长路径涡所伴的正涡度柱比短路径涡深厚,上升运动柱比短路径涡强;长路径涡所伴的正涡度柱随高度升高向北倾斜、涡度值上小下大,不同于短路径涡呈对称分布、涡度值上大下小;长路径涡所伴的南风中心位置比短路径涡偏东,东、西风交汇位置比短路径涡更偏南、更强;长路径涡加强时涡区上空正涡度平流中心位置比移出时下降、强度加强,且持续时间长、向东偏离低涡,短路径涡则相反。(3)长、短路径涡在不同演变中,低涡的强度变化是由输入涡区的正涡度平流支撑的。长、短路径涡加强时的结构特征差异体现了长路径涡蕰含涡度增加的垂直输送机制和正涡度平流强迫上升运动增强而使低涡加强的动力机制。

     

    Abstract: Herein, a comparative analysis was conducted on the structural characteristics of high-impact eastward-moving Qinghai–Tibet Plateau vortices (TPVs) with quasi-straight long paths (QSLTPVs) and quasi-straight short paths (QSSTPVs) by adopting a dynamic composite method of the TPV in the moving accompanying the TPV. The analysis considered the warm season months from May to September, spanning from 1998 to 2018. To conduct this study, various data sources, including global analysis data obtained from NCEP/NCAR, atmospheric observational data, and the TPV and shear line yearbooks. The relationship between the intensity and structure of QSLTPVs and QSSTPVs was studied, revealing that their evolution is determined to some extent by the structure of the low vortex itself. The key findings of this analysis are as follows: (1) Both QSLTPVs and QSSTPVs exhibit similar structural characteristics. Initially, they form as shallow weather systems and evolve into deeper weather systems upon exiting the Tibetan Plateau, which is a trend consistent with that of the vorticity of low vortices in different activity stages. (2) The structural differences between QSLTPVs and QSSTPVs become apparent during their strengthening stage. QSLTPVs exhibit a thicker positive vorticity column and a stronger ascending motion column compared with those of QSSTPVs. Furthermore, the positive vorticity column of QSLTPVs tilts northward as the height ascending, exhibiting smaller vorticity in the upper layer and larger vorticity in the lower layer. Meanwhile, the positive vorticity column of QSSTPVs display a symmetrical distribution and a vertical vorticity distribution opposite to that of QSLTPVs. In addition, the center of the south wind associated with QSLTPVs is positioned more easterly and the confluence position of easterly and westerly winds is more southerly and stronger compared to the case of QSSTPVs. After departing from the Tibetan Plateau, the center of positive vorticity advection overlying the vortex area of QSLTPVs is lower, the intensity of the advection is strengthened, and the advection lasts longer, deviating to the east of QSLTPVs; meanwhile, QSSTPVs exhibit the opposite pattern. (3)The varying intensities of low vortices during the evolution of QSLTPVs and QSSTPVs are underpinned by the positive vorticity advection of the input vortex regions. The structural differences in the strengthening stage reflect that QSLTPVs incorporate a vertical transport mechanism that increases vorticity and a dynamic mechanism that enhances the forced ascending motion of positive vorticity advection, thereby facilitating the strengthening of the TPVs.

     

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