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东北冷涡背景下同一线状风暴内两类γ中尺度涡旋的观测特征研究

Analysis of the observational characteristics of two types meso-γ-scale vortices in the same linear storm under the background of Northeast China Cold Vortex

  • 摘要: 2024年7月24日凌晨,线状风暴内同时出现了两类γ中尺度涡旋,即中气旋和中涡旋,导致辽宁省出现短时强降水和雷暴大风。本文利用探空观测、气象观测站、双偏振雷达和ERA5再分析资料,研究此次过程的影响系统和环境条件、不同类型γ中尺度涡旋的动力和微物理特征,并给出该风暴内不同类型γ中尺度涡旋处短时强降水和雷暴大风的物理模型。结果表明:(1) 此次过程中辽宁省位于东北冷涡底部,具有超过1 000 J·kg−1的CAPE和强垂直风切变。23日夜间形成线状风暴并向东南方向移动,其右侧出现中气旋,前侧存在低层辐合带。(2) 该风暴与左前方的风暴在低层初次合并,辐合带上生成低空浅薄的中涡旋(MV)。此时中气旋和MV附近存在差分反射率因子(Zdr)和差分传播相移率(Kdp)高值区,但并未重合,监测到强对流的站次较少。(3) 随后线状风暴与前侧风暴在MV上空再次合并,MV垂直伸展且旋转加强。MV通过冰相过程形成更大的降水粒子,同时增加风暴内雨水输送机制,MV和辐合带之间出现ZdrKdp高值区增加且接近的现象,因此5 min内强对流站次出现增加的现象。(4) 强降水发生时,整层反射率因子和Kdp平均值比雷暴大风高,而Zdr偏低;而雷暴大风发生时,冷云层6 km处的Zdr较强降水高0.3 dB,而3.5 km到近地面,各参量随高度下降存在更明显降低的现象。研究可为提升东北冷涡背景下γ中尺度涡旋相关的强对流天气的预警能力提供参考。

     

    Abstract: During the early morning of 24 July 2024, a mesocyclone and a mesovortex co-occurred within a linear storm produce short-duration heavy rainfall and thunderstorm gales in Liaoning Province. This study investigates the observed evolution and environmental conditions of this event, as well as the kinematic and microphysical characteristics of different types of meso-γ-scale vortices by analyzing sounding observations, automatic weather station data, dual-polarization radar, and ERA5 reanalysis data. Ultimately, a physical model for short-duration heavy rainfall and thunderstorm gales associated with these meso-γ-scale vortices within the storm is proposed. The result are as follows. (1) Liaoning Province was located at the southern periphery of the Northeast China Cold Vortex (NCCV), characterized by convective available potential energy exceeding 1 000 J·kg−1 and strong vertical wind shear. During the night of 23 July, a linear storm formed and moved southeastward, with a mesocyclone developing on its right flank and a low-level convergence zone present at its leading edge. (2) The linear storm initially merged with a cell to its left-front at low levels, triggering the genesis of a shallow low-level mesovortex (MV) along the convergence zone. At this stage, regions with high differential reflectivity (Zdr) and specific differential phase (Kdp) existed near both the mesocyclone and the MV. The high-value areas of Zdr and Kdp were in the lower layer of the storm and not coincident, there were fewer strong convective weather at this time. (3) The linear storm and the frontal storm merged again over the MV, and the MV showed characteristics of bottom-up development and increased rotational speed. MV formered larger particles through the ice phase process, while increasing the mechanism of rainwater transport within the storm. There was a phenomenon of increasing and approaching high values of Zdr and Kdp between MV and the convergence zone. Consequently, there was an increase in the number of stations reporting severe convection within 5-min intervals. (4) During heavy rainfall, the column-averaged reflectivity and mean Kdp were higher than those during thunderstorm gales, while Zdr was relatively lower. In contrast, during thunderstorm gale events, the Zdr at 6 km within the cold cloud layer was 0.3 dB higher than that during heavy rainfall, and these polarimetric variables exhibited a more pronounced decrease with decreasing altitude from 3.5 km down to the surface. The findings of this study can provide reference for improving the early warning capabilities for severe convective weather associated with meso-γ-scale vortices under the background of NCCV.

     

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