Microphysical characteristics of precipitating cumulus cloud based on airborne Ka-band cloud radar and droplet measurements

Based on cloud-probe data and airborne Ka-band cloud radar data collected in Baoding on 5 August 2018,the microphysical structural characteristics of cumulus(Cu)cloud at the precipitation stage were investigated.The cloud droplets in the Cu cloud were found to be significantly larger than those in stratiform(STF)cloud.In the Cu cloud,most cloud particles were between 7 and 10μm in diameter,while in the STF cloud the majority of cloud particles grew no larger than 2μm.The sensitivity of cloud properties to aerosols varied with height.The cloud droplet effective radius showed a negative relationship with the aerosol number concentration(Na)in the cloud planetary boundary layer(PBL)and upper layer above the PBL.However,the cloud droplet concentration(Nc)varied little with decreased Na in the high liquid water content region above 1500 m.High Na values of between 300 and 1853 cm-3 were found in the PBL,and the maximum Na was sampled near the surface in August in the Hebei region,which was lower than that in autumn and winter.High radar reflectivity corresponded to large FCDP(fast cloud droplet probe)particle concentrations and small aerosol particle concentrations,and vice versa for low radar reflectivity.Strong updrafts in the Cu cloud increased the peak radius and Nc,and broadened cloud droplet spectrum;lower air temperature was favorable for particle condensational growth and produced larger droplets.

Revisiting the size of nonspherical particles recorded by optical array probes with a new method based on the convex hull

In recent years,the Cloud Imaging Probe(CIP)and Precipitation Imaging Probe(PIP)produced by Droplet Measurement Technologies(DMT)have been introduced by a number of meteorological research and operation centers in China.The supporting software provided by DMT,i.e.,PADS(Particle Analysis and Display System),cannot output detailed information on each individual particle,which definitely limits the in-depth utilization of cloud and precipitation particle image data in China.In this paper,particle-by-particle information was extracted by decompressing the CIP and PIP original particle image data,based on which a new definition of the dimension for nonspherical particles is proposed by using the area of the convex hull enclosing a particle to obtain the equivalent diameter of a circle with equal area.Based on the data detected during one flight in Inner Mongolia,the particle size distribution obtained using the new particle size definition and that used by the other four existing definitions are compared.The results show that the particle number concentration calculated using different particle size definitions can vary by up to an order of magnitude.The result obtained based on the new particle size definition is closest to that calculated with the area-equivalent diameter definition.

Evaluation of a Lagrangian advection scheme for cloud droplet diffusion growth with a maritime shallow cumulus cloud case

A Lagrangian advection scheme(LAS)for solving cloud drop diffusion growth was previously proposed(in 2020)and validated with simulations of cloud droplet spectra with a one-and-a-half dimensional(1.5D)cloud bin model for a deep convection case.The simulation results were improved with the new scheme over the original Eulerian scheme.In the present study,the authors simulated rain embryo formation with the LAS for a maritime shallow cumulus cloud case from the RICO(Rain in Cumulus over the Ocean)campaign.The model used to simulate the case was the same 1.5D cloud bin model coupled with the LAS.Comparing the model simulation results with aircraft observation data,the authors conclude that both the general microphysical properties and the detailed cloud droplet spectra are well captured.The LAS is robust and reliable for the simulation of rain embryo formation.