基于多源观测资料的江淮气旋北部层状云系宏微观特征

Macro- and micro-structures of stratiform cloud systems in the northern region of the Yangtze-Huaihe cyclone based on multi-source observations

摘要:

基于卫星、组网天气雷达、毫米波云雷达和飞机等观测资料以及ERA5再分析资料,对2023年4月4日河北南部一次层状云降水过程进行分析。结果表明,此次降水过程是高空槽、江淮气旋以及低空急流共同影响下的江淮气旋北部层状云降水过程。云系结构分析表明,江淮气旋进入成熟阶段后,云系向东北方向移动,云顶高度介于8至11 km,云系发展深厚。在降水发展时段,云中冰相粒子占主导地位,微物理转化过程主要涉及冰晶的凝华增长、聚并增长以及淞附增长。在降水消散时段,云中同样以冰相粒子为主,但云顶和云底降低,冰晶层变得浅薄,云中存在冰晶繁生过程。

Abstract:

This study investigates the macro- and micro-physical characteristics of a stratiform precipitation event in southern Hebei on April 4,2023,influenced by a combination of a high-altitude trough,the Yangtze-Huaihe cyclone,and a low-level jet stream.Leveraging data from the Luancheng Cloud Microphysics Superstation,aircraft observations,operational weather radar,and satellite imagery,the research provides a comprehensive analysis of the cloud microphysical and precipitation processes.The precipitation event,located north of the Yangtze-Huaihe cyclone,was driven by dynamic interactions between a low-level jet at 850 hPa,a high-altitude trough at 500 hPa,and a reversed trough at 700 hPa.These conditions created upper-level divergence and lower-level convergence across Hebei Province,facilitating the large-scale ascent of warm,moist air and the formation of a stratiform cloud system.Analysis of radar reflectivity and FY-4B satellite data,including cloud-top height and blackbody brightness temperature,indicated that the Yangtze-Huaihe cyclone reached its mature stage on April 4,displaying a typical “comma-shaped” cloud structure that moved northeastward over time.The stratiform cloud region north of the cyclone exhibited cloud-top brightness temperatures ranging from -10 ℃ to -25 ℃,within the “cloud seeding temperature window.” Cloud-top heights ranged from 8 to 11 km,indicating a deep and well-developed cloud system.During the precipitation development phase,the cloud system consisted primarily of ice-phase particles.Above 3.8 km,ice crystals dominated,originating from small ice crystals falling from the convective region and nucleated ice crystals in the stratiform cloud.These crystals underwent slow deposition growth as they descended.Between 1.8 and 3.8 km,the cloud radar reflectivity factor increased significantly,reflecting processes such as deposition growth,aggregation,and riming of ice crystals.Below 1.8 km,precipitation transitioned to rain as ice crystals melted upon exiting the cloud layer.In the dissipation phase,cloud-top and cloud-base heights decreased,and the ice crystal layer thinned.After 12:00 BST,a shift in high-altitude wind direction to the west dispersed upper-level ice crystals,inhibiting further deposition growth and reducing cloud-top height and ice crystal content.Deposition growth remained dominant above 3.8 km,while aggregation and rimming prevailed between 1.0 and 3.8 km,with fragmentation observed in the 2.8—3.8 km range.During this phase,relatively low liquid water content limited the precipitation process,diverging from the typical “seeding-supply mechanism”. This study provides valuable insights into the cloud microphysical processes associated with stratiform precipitation,offering a basis for monitoring and identifying conditions suitable for artificial weather modification.While the findings enhance understanding of weather modification conditions,they are based on a single case.Future studies should expand to multiple cases to refine the understanding of cloud structures and precipitation processes,ultimately improving the scientific foundation for artificial weather modification operations.