A Study Of Meteorological Radar Detection Of Cloud-rain Turbulence And Microphysical Parameters

Turbulence is considered as an important factor influencing the formation and development of cloud and rainfall,which is closely related to the complex microphysical process.In this paper,L-band boundary layer wind profiler radar and Ka-band millimeter-wave cloud radar measurements were used to retrieve and analyze the microphysical parameters and turbulence characteristics in rainfall and cloud respectively.On the one hand,the microphysical parameters of raindrops and the turbulent dissipation rate in rainfall were retrieved by separating the bimodal-shaped power spectrum data of wind profiler radar,and the relationship between them was analyzed preliminarily.On the other hand,the turbulence characteristics of different cloud types were analyzed by using the millimeter wave cloud radar power spectrum data,and the retrieval error of the turbulent dissipation rate was evaluated.Then the cloud microphysical parameters were retrieved,and the relationship of microphysical parameters to in-cloud turbulence was studied and analyzed.The main conclusions are as follows:(1)In raifall,small raindrops got enlarge through collision-coalescence in weak turbulence,but large raindrops broken-up into small drops under strong turbulence,and the separation value of turbulence being weak or strong varies with the rainfall attributes and stages,for example,it is about 10^-2.4m²/s³in the mixed type rainfall and 10^-1.8m²/s³in the stratiform rainfall.(2)The in-cloud turbulence can increase the spectral width,and promote the coalescence of small cloud droplets,which makes the cloud droplets large and the number concentration decrease.In addition,the Doppler velocity spectrum has a-5/3 slope in the high frequency region,which is consistent with Kolmogorov theory.Under weak turbulence,it is greatly affected by the noise,and the fractional error of the turbulence dissipation rate is large.(3)The case study shows that the overall value of turbulent dissipation rate in rainfall is relatively large,ranging from 10^-3.5to 10^-1m²/s³,and positively correlated to the velocity spectrum width.The turbulent dissipation rate in the cloud is about 10^-8?10^-1m²/s³,which is usually strong near cloud base or cloud top.When the cloud layer is thin,the distribution of turbulence may uniform.In the weak precipitation process,the in-cloud turbulence will increase rapidly before precipitation,and the turbulence in the process of precipitation is strong and evenly distributed.Then,with the weakening of turbulence,the cloud will gradually dissipate,and the precipitation stops.(4)Turbulence has two main effects on the formation and development of cloud and rainfall:turbulence can increase the collision efficiency of droplets,promote the collision-coalescence and fragmentation of particles;turbulence also can strengthen the transport of heat,water vapor and other substances,and may strengthen evaporation,resulting in the slow change of water content.