广西“6·13”强降水过程低空急流的作用及其日变化成因

doi:10.3969/j.issn.1673-503X.2024.05.001

摘要/Abstract

摘要：

利用实况观测以及ERA5再分析资料, 对2022年广西“6·13”强降水过程进行了分析诊断, 并着重分析了低空急流的作用及其日变化成因。结果表明: 强降水过程受高空槽、低层切变线以及西南低空急流共同影响。低空急流日间减弱而夜间明显增强, 在切变线南侧的急流顶端不断有对流系统发生发展, 造成强降水主要集中于夜间。极端强降水出现在中尺度对流云团合并阶段, 落区位于TBB梯度大值区。夜间低空急流左前方辐合和山脉地形阻挡共同作用使得低层辐合增强, 促进上升运动发展。低空急流夜间增强使得冷暖空气在桂东北一带剧烈交汇, 导致低层水平锋生强迫增强, 有利于降水维持和增强。在低空急流持续暖湿输送下, 大气低层不稳定结构明显增强, 为对流系统以及强降水提供有利的发展维持环境。此外, 夜间低空急流推动水汽在桂东北一带辐合抬升, 与强降水落区具有较好对应。动量收支诊断表明, 惯性振荡是造成低空急流日变化的主要机制。夜间科氏力对非地转风的作用主导了动量变化, 非地转风顺时针旋转为西南风, 与背景风场叠加进而增强了低空急流; 日间湍流摩擦增强, 残差项和平流项共同耗散局地动量。

关键词: 低空急流, 锋生强迫, 动量收支, 惯性振荡

Abstract:

Based on observation data and ERA5 reanalysis data, an analysis and diagnosis of thes "6·13" heavy rainfall process in Guangxi in 2022 were conducted, with a focus on the role of diurnal variation and its cause of low-level jet. The results show that the heavy rainfall process is jointly influenced by the upper level trough, the low-level shear line and the southwest low-level jet. The low-level jet weakens during the day and significantly strengthens at night, with convective systems continuously developing at the top of the jet and the south of the shear line, resulting in heavy rainfall mainly concentrated at night. The extreme heavy rainfall appears during the merging stage of mesoscale convective cloud clusters, located in the large TBB (Top Blackbody Brightness temperature) gradient region. The convergence in the left front of the low-level jet at night and the obstruction of mountain topography together enhance the low-level convergence and promote the development of upward movement. The intensification of low-level jet at night causes the intense convergence of warm and cold air in the northeastern region of Guangxi, resulting in the enhancement of low-level horizontal frontogenesis forcing, which is conducive to the maintenance and intensification of precipitation. Under the continuous warm and humid transport of the low-level jet, the unstable structure in the lower atmosphere is significantly enhanced, which provides a favorable environment for the development and maintenance of convective systems and heavy rainfall. In addition, the low-level jet promotes the water vapor convergence and uplift in the northeastern region of Guangxi at night, which corresponds well with the heavy rainfall area. The diagnosis of momentum balance shows that inertial oscillation is the main mechanism causing the diurnal variation of low-level jet. The Coriolis force at night dominated the momentum change of the geostrophic wind, which rotates clockwise to form the southwest wind and superimposes with the background wind field to strengthen the low-level jet. The daytime turbulent friction is enhanced and the residual and advection terms jointly dissipate local momentum.

Key words: Low-level jet, Frontogenesis force, Momentum balance, Inertial oscillation

中图分类号:

P426.62

覃皓,刘乐,农孟松. 广西“6·13”强降水过程低空急流的作用及其日变化成因[J]. 气象与环境学报, 2024, 40(5): 1-11.

Hao QIN,Le LIU,Mengsong NONG. The role of low-level jet and its cause of diurnal variation during the "6·13" heavy rainfall process in Guangxi[J]. Journal of Meteorology and Environment, 2024, 40(5): 1-11.

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