Processing method for the partial particles and its influence on the cloud microphysical parameters measured by the airborne cloud and precipitation image probe

Abstract

As an important instrument for the cloud microphysics measurement, the airborne cloud and precipitation imaging probe plays a significant role in studying the cloud and precipitation physics and artificial weather modification. The particle image data recorded by the probe can be used to process, calculate and produce the cloud microphysical parameters, such as the cloud particle size spectra, cloud particle number concentration, cloud water content, etc. However, there are lots of partial particle images in the sampled data. This is due to the limited sample volume of the probe, the volume that contains only a part of the particles and is imaged by the probe. The number of partial particles in each sample is so large that the technique used to process these particles can have a great influence on the calculation of cloud microphysical parameters. However, there has been no perfect solution for dealing with these partial particles so far.<br/>The three existing processing methods-“All In” method, “Center In” method, and “Diameter Reconstruction” method for the partial particles, are introduced and analysed in this study. After analyzing the advantages and disadvantages of these existing methods, a new definition and a particle shape classification for the partial particle are given, which can discriminate the circularly symmetric particles and the non-circularly symmetric particles from the partials. Then a new partial particle processing method is introduced, which combines the partial particle shape recognition technique and the traditional techniques-“Center In” method and “Diameter Reconstruction” method. The circularly symmetric partial particles are processed with the “Diameter Reconstruction method” and the non-circularly symmetric partial particles are processed with the “Center In” method.<br/>Utilizing the historical airplane observation data from Shanxi Taiyuan, the new method presented in this study and the three traditional methods are used to calculate the cloud particle size spectra, cloud particle number concentration, and the ice water content by using the same data. The calculated results are analyzed and compared. It is found that in most cases the results from the new method are more consistent with those from the “Diameter Reconstruction” technique and can overcome the disadvantages of the existing methods, especially when the cloud has more column-shaped and needle-shaped particles, the result from the new method is more reasonable. Considering the fact that the column shape is one of the main shapes in the cloud, it is strongly recommended to use the new technique in this paper to process the data from the probes.