一次基于飞机观测的低槽冷锋云系微物理结构的综合分析

A comprehensive analysis of the physical structure of a low trough cold front cloud system based on aerial observation

针对2012年9月25日山西一次低槽冷锋层状云,组织有设计的飞机观测,通过斜飞、螺旋、分层探测等方式,实现对云微结构的精细观测,同时结合卫星、雷达、探空等资料进行该云系的综合分析。结果显示:1)本系统为冷暖混合层状云系,云中无明显夹层,云系宏、微观结构均匀、稳定,地面有明显降水。2)冷云区多为固态冰相粒子,以凝华增长为主,过冷水欠缺;小云粒子谱呈指数分布,大云粒子谱呈双峰分布,降水粒子谱呈三峰分布;云中相同高度的不同位置上,粒子谱型、浓度基本一致。3)暖云区大云粒子和降水粒子的谱宽较冷云区变窄,谱型由多峰变为单峰。随高度下降,降水粒子有效直径变大、浓度变小,其垂直分布同雷达回波的垂直剖面相吻合。4)地面降水主要是由冰相粒子增长造成,本次过程冰相粒子充分、过冷水缺乏,因此该层状云引晶催化的潜力较小。

A comprehensive set of aircraft-based aerial observations of the physical structure of a low trough cold front stratiform cloud was organized on 25 September 2012 in Shanxi Province.Combined with satellite and other data, the main results were as follows： The system was a mixed system with no interlayer.The cloud physical structure was uniform and stable.Rain- fall was obvious on the ground.The detection area was mainly ahead of the trough at 500 bPa and 700 hPa, and behind the cold front on the ground.The height of the cloud top was 10--13 km.The temperature of the cloud top is -40 to -50 ~C.The height of the 0 ^（2 layer was 4 000 m. The cloud physical parameters obtained from satellite and radar changed little along with space and time.In cold cloud region, there is hardly any supercooled water, but mainly ice-phase particles, which grow lager by con- densation process.The spectrum of cloud droplet probe （in short, CDP, range from 2--50 Nm） detection showed a exponential distribution.The spectrum of cloud image probe （ in short, CIP, range from 25-- 1 550 Ixm） detection showed a bimodal distribution.The spectrum of precipitation image probe （in short, PIP, range from 100--6 200 txm） detection showed a trimodal distribution.The particle spectrum type and concentration was uniform in differ- ent positions at the same height in the cold zone.The distribution of the microphysical parameters was uniform in the cold zone.Ice particles fell into the 0 ~C layer and began to melt, and then the particle phase state shifted.The spectral width of CIP and PIP turned narrow in the warm zone, and their spectrum type turned unimodal.PIP was concentrated under 2 000 ixm.The CDP spectrum was unimodal near 0 ~C .The concentration of CDP and CIP was largest near the 0 ~C layer, and another high concentration area of these parameters occurred around the height of 1 500 m.The max concentration of PIP appeared at 6 300 m,The concentration is fewer, while the effective diam- eter is bigger with the reduced height, which is caused by cloud physical processes, such as coagulation.The phe- nomenon is consistent with the vertical radar echo structure.Calculating the radar echo on the aircraft flight path revealed that CIP and PIP were larger than their measured values.The vertical growth rate of the radar echo values from high to low was approximately 5 dBz ~ km-1. Based on the analysis, the microphysical structure of the cloud system was uniform and stable, and lacked su- percooled water. In this kind of cloud, the potential for precipitation enhancement is small;rainfall on the ground is mainly caused by ice particles.This paper provides some evidence for the seeding index during precipitation en- hancement operation.However,this is just a case study, and more statistics analysis should be supplement in the future.Additionally ,the design of the flight path needs further consideration.