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2413号台风“贝碧嘉”引发安徽强降水的特征及预报偏差分析

Analysis of characteristics and forecast bias of heavy rainfall induced by typhoon Bebinca (2413) in Anhui Province

  • 摘要: 2024年第13号台风“贝碧嘉”在上海登陆后逐渐向西北移动,经江苏省以强热带风暴级移入安徽省境内,在安徽引发了持续性强降水过程。此过程可分为两个阶段:第一阶段,安徽省出现大范围强降水;第二阶段,台风减弱至热带低压强度后,在安徽北部引发局地极端强降水。本文基于多源观测资料、ERA5再分析数据及数值模式预报资料,对比分析了两个降水阶段的环境条件、中尺度对流系统及降水微物理特征,并探讨了第二阶段降水模式预报偏差较大的原因。主要结论如下:(1) 两阶段强降水均以高浓度的小粒子为主,偏向于热带海洋性降水。大量小粒子在下落过程中发生碰撞—碰并增长,导致地面降水中出现较大粒子。(2) 第一阶段,台风东南象限存在强上升运动与水汽辐合区,随着台风西北行,在安徽引发大范围强降水。第二阶段,台风减弱为热带低压,上升运动和水汽辐合区移至安徽北部但强度弱于第一阶段,中低层上升区随高度向北倾斜。(3) 受螺旋雨带影响,安徽北部形成具有“列车效应”的带状回波。持续高效的暖云降水过程,致使该地区在第二阶段出现局地极端降水。(4) ECMWF预报的台风中心位置偏西,且台风北部底层偏北风较强,使得第二阶段强降水落区预报偏西。随着中尺度对流被触发,潜热释放过程可进一步加剧模式预报偏差。

     

    Abstract: After making landfall in Shanghai, Typhoon Bebinca (2413) gradually moved northwestward. It entered Anhui Province from Jiangsu Province at severe tropical storm intensity and induced a persistent heavy rainfall process in Anhui. This process can be divided into two stages: in the first stage, widespread heavy precipitation occurred across Anhui Province. in the second stage, after the typhoon weakened to a tropical depression, localized extreme heavy precipitation was triggered in northern Anhui. Based on multi-source observational data, ERA5 reanalysis data, and numerical model forecast products, this study compares the environmental conditions, mesoscale convective systems, and precipitation microphysical characteristics of the two rainfall stages, and explores the causes of the significant forecast bias of the model in the second stage. The main conclusions are as follows. (1) The heavy precipitation in both stages was dominated by high concentrations of small particles, indicative of tropical maritime precipitation. A substantial number of small particles grew through collision-coalescence during their descent, leading to the presence of larger particles in surface rainfall. (2) In the first stage, strong upward motion and water vapor convergence were present in the southeastern quadrant of the typhoon. As the typhoon moved northwestward, it triggered widespread heavy precipitation in Anhui. In the second stage, after the typhoon weakened to a tropical depression, the upward motion and water vapor convergence zones shifted to northern Anhui but were weaker than in the first stage, and the mid-to-low-level upward motion zone tilted northward with height. (3) Influenced by spiral rainbands, banded echoes exhibiting the train effect formed over northern Anhui. The sustained, efficient warm-cloud precipitation process led to localized extreme heavy precipitation in this region during the second stage. (4) The ECMWF model forecast showed a westward bias in the typhoon center position, with stronger low-level northerly winds to the north of the typhoon, resulting in a westward bias in the forecast heavy precipitation area for the second stage. Once mesoscale convection was triggered, the latent heat release further amplified the model forecast bias.

     

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