三江源层状云系微物理结构特性的飞机观测研究

Microphysical structural characteristics of stratiform clouds over the Sanjiangyuan National Nature Reserve:insights from airborne observation

摘要:

利用机载粒子测量系统(particle measuring system,PMS)对三江源一次春季典型层状云系进行分层垂直探测,研究了云系的微物理结构特性。结果表明,春季典型层状云系由3层云层组成,卷层云(Cs)为冰云,分为上、下两层的高层云(As)为过冷混合态云,过冷水高值区位于下层高层云的中上至中下部位,在其中下部过冷水含量及云粒子浓度最大,具有较明显的地区特性。过冷水高值区的液态云粒子主要是中值直径在3.5～27.5 μm范围内的云滴,30.5 μm以上云粒子基本上为冰相。在下层高层云中上部的过冷水高值区有较明显的淞附增长现象,而中下部存在较明显的冰晶效应。在下层高层云过冷水高值区,过冷水含量比率的平均值达(90.8％±10.9％),且其中部至中下部位处(95.6％±5.6％)明显高于中上部(79.8％±12.1％),为人工增雨作业催化提供了有利条件。

Abstract:

Cold front precipitation cloud systems are the primary target for ecological restoration through artificial precipitation enhancement in the Sanjiangyuan National Nature Reserve.However,the quantitative understanding of these cloud systems remains insufficient.Aircraft observations are currently the only method to directly obtain the phase state of cloud particles,making them a crucial component of cloud and precipitation physics studies.In this study,we analyzed the microphysical characteristics of a typical layered cloud system in the Sanjiangyuan region during spring,based on vertical detection data collected using the particle measurement system (PMS).To discriminate the phase state of cloud particles,the study adopted 2DC image gray projection data,identifying discriminate non-spherical cloud particles with sizes between 50 μm and 125 μm as ice crystals.The criteria for phase discrimination included: i) mean diameter N_2(>50)> 0.1 L^-1,and ii) the water content LWC_FSSP> 10^-3 g/m³.Flight observations revealed a three-layered stratiform cloud system during spring;i) cirrostratus (Cs) located at an altitude of about 7 400—7 800 m above sea level with a thickness of 300—400 m,consisting entirely of ice-phase clouds,ii) upper and lower layers of altostratus (As) positioned between 6 400—6 600 m above sea level,and 5 100—6 200 m above sea level,respectively.The results show that the high supercooled water regions were primarily distributed in the middle,upper,and lower parts of the low-level As layer.These regions exhibited the highest cloud particle concentrations and supercooled water contents,with distinct regional characteristics.The average cloud particle concentration As measured by FSSP in the studied region was significantly higher than that of stratiform clouds in inland northern China and higher than autumn observation in this region.This regional distinction is largely attributed to the abundant water vapor in the Sanjiangyuan region.The liquid cloud particles in the As layer were predominantly concentrated within a median diameter range of 3.5—27.5 μm,while particles exceeding 30.5 μm were primarily ice-phase.In the middle and upper parts of the low As layer,there was pronounced growth in the high supercooled water region,with ice crystal formation and growth predominantly occurring in the middle and lower parts.In the low supercooled water regions,the average supercooled water content ratio was (90.8％±10.9％).The ratio in the middle to lower parts (95.6％±5.6％) was significantly higher than in the middle and upper parts (79.8％±12.1％).As the primary precipitation-generating cloud layer,accretion growth in the lower As layer was the dominant mechanism for the generation of large-size ice particles.These findings underscore the importance of accurate characterization and understanding of the microphysical structure of the layered cloud system in Sanjiangyuan.Such insights provide a reliable observation basis for the optimizing artificial precipitation enhancement operations in the region.This study has significant practical significance for advancing the understanding of the microphysical characteristics of stratiform clouds in Sanjiangyuan and improving aircraft-based artificial precipitation operation technologies.