Observational And Inversion Of The Terminal Fall Velocity Of Ice Cloud Particles At The SACOL

Ice clouds cover nearly 30%of the world,which have an important impact on the energy budget of local and global earth gas systems.The change of ice cloud life cycle largely determines the climate radiation effect of ice cloud.The terminal fall velocity of ice cloud particles is the key parameter affecting the life cycle of ice cloud.A clear understanding of the macro-micro-physical properties of ice clouds is of great significance for the simulation and prediction of climate change.The Doppler cloud radar is an effective tool for observing and studying ice clouds because of its unique advantages.Lanzhou University Semi-Arid Climate and Environment Observatory(SACOL)introduced the first Ka-Band Zenith radar(KAZR)in July 2013 and has been running for nearly seven years.By using continuous observations of the Ka-band millimeter-wave cloud radar from August 2013 to July 2015,we retrieved the particle terminal fall velocity and calculated the values of the coefficients a and b based on the relationship between the radar reflectance factor Z and Vt.Then,we further divide the ice clouds into four categories by clustering analysis,and discuss the spatiotemporal distribution of the reflectivity,the terminal fall velocity,coefficients a and b of the four different types of ice cloud.Furthermore,we try to study the change of microphysical processes in different positions in the cloud through the parameter vertical distribution feature recognition.Here are some main conclusions:(1)Different inversion algorithms can obtain the particle terminal fall velocity well.The results of the statistical fitting algorithm filter out the air moving part well,but because the difference of cloud physical properties in the vertical direction is not considered,there is also a large value in the top part of the cloud.Because it can only be applied to the environment field without large-scale vertical motion,the time average method results in a negative value at the higher position of the clouds Combined with the former two methods,the joint inversion algorithm first avoids the assumption of cloud homogeneity,and removes the negative part of Doppler velocity in the result,so that the velocity of cloud top is close to zero,and some large value areas in the cloud are reserved,which is closer to the real situation(2)The ice cloud in sacol station is mainly concentrated in the range of 2km-12km.The distribution range of radar reflectivity of SACOL station is-53.4 dBZ to 9.3 dBZ,the maximum frequency is concentrated in the range of-30 dBZ to-15 dBZ,and the maximum frequency of the particle terminal fall velocity is concentrated in the range of 0.3m/s to 0.5m/s.The results show that the distribution of Vt corresponds well to Z,and the maximum frequency appears about 7km near the ground.In addition,they all show significant seasonal changes and the terminal fall velocity can be increased by 25%in the warm season compared to the cold season,mainly because the rising motion is strengthened because of the high temperature in warm season,which is not only beneficial to the formation of cloud,but also the increase of cloud particle will increase its terminal fall velocity accordingly(3)The average values of radar reflectivity factor,particle terminal fall velocity and fitting coefficient a and b of the first and third types of ice clouds with thicker clouds and longer duration are significantly larger than those of the second and fourth types of clouds with thinner clouds and shorter duration.The first and third types of thick clouds have a long duration,so their daily changes are relatively gentle and their fluctuations are not large.The parameters of all types of ice clouds are relatively consistent in seasonal changes,all peaking in June and September.(4)In the vertical direction,Z,Vt and fitting coefficient b from the top of the cloud to the bottom of the cloud show a tendency to increase first and then decrease with the decrease of the height of the cloud,which reflects the microphysical processes at different locations in the cloud.In the top part of the cloud,the nucleation of particles and the deposition of water vapor in the cloud are dominant.With the decrease of cloud height,the deposition of water vapor and the aggregation of particles play a major role,the cloud particles gradually increase.In the cloud layer close to the cloud bottom,the cloud particles evaporate and sublimate,and the particle size decreases.While the distribution characteristics of fitting coefficient b in the vertical direction also indicate that this parameter can be tried for the identification of different physical processes within the cloud.