Studies Of Cloud Macro-and Microphysical Properties Using China New Generation Millimeter-Wavelength Radar

In comparison with widely used centimeter wavelength radars, millimeter wavelength radars have certain advantages for detecting nonprecipitating and lightly precipitating clouds. The sensitivity to small hydrometeors and excellent spatial resolution make them provide important information about the macro and micro cloud properties. Data with a35GHz dual-polarization Doppler radar (HMBQ) is studied to analyze the qualitative information about the presence of clouds and to develop a method to retrieve cloud microphysical properties. The main contents and conclusions are as follows:(1) The general development and main advantage of millimeter wavelength radars is summarized. Furthermore, the components and parameters of HMBQ are introduced in order to evaluate its detecting capability. In addition, the results from recent cloud experiments are presented to reveal the intricate structure of a wide variety of clouds obtain by HMBQ.(2) The capacity of HMBQ was investigated based on an aircraft and cloud radar co-observation. The reflectivity calculated from aircraft measurements is compared with the simultaneous radar observation in detailed. It shows that the two reflectivities are comparable in warm clouds, but in ice cloud there are more discrepancies which are probably associated with the occurrence of overcooled liquid water. Because of the difficulty of exactly matching up the collocation between the two sensors and their distinct sample volumes, the deviation is inevitable. Based on the dataset collected in warm clouds in this experiment, the threshold of reflectivity to diagnose drizzle and cloud particles is studied by analyses of the probability distribution function of reflectivity due to cloud particles and drizzle drops. The reflectivity of cloud particles is usually below-5dBZ which the value of drizzle is above-20dBZ. A value between-15and-12dBZ can be used as the threshold of drizzle.(3) Determination of cloud base and top heights from millimeter wavelength radar are compared to those from the Micro Pulse Lidar (MPL) as a means to evaluate the accuracy of both cloud radar and MPL retrievals, as well as to ascertain their limitations. Four cases are studied, including a stratocumulus, a altostratus, a altocumulus and a cirrocumulus. The study reveals that the cloud boundaries detected by both cloud radars agree well with each other. However, the MPL usually reports higher cloud base heights than cloud radar. Statistical comparison reveals that the differences between their mean cloud base heights are large for nonflat-based altostratus but small for other cases. The differences are mainly due to the different scattering mechanism for light and microwave and the distinct methods of cloud boundaries identification. The MPL sometimes see higher cloud tops than the cloud radar when the lidar signal can completely penetrate the clouds. However, for deeply developed clouds the cloud radar measure reliable cloud tops while MPL suffers heavy attenuations. Furthermore, the MPL has a superior in some optical thin clouds detection. An integration of cloud boundary is determined based on these analyses. Using the radar/lidar synergetic observations, frequency distributions of cloud macro structure are calculated.(4) A detailed description of the Doppler spectra is given in theory. One size particles in the radar resolution volume produce a uni-mode Gaussian spectrum. Different size particles produce a spectrum that is due to the linear superposition of their Gaussian signals. Several examples of Doppler spectra detected by HMBQ are presented to show that the structures of Doppler spectra bring information on the size range of droplets. Commonly double-model structures are related to cloud droplets of different size, ice crystals with different habit and size, or cloud droplets mixed with ice crystals. In order to evaluate the moments of the Doppler spectra due to different ensembles of particles, a method of decomposing Doppler spectra is applied. Firstly, the measured spectra are averaged over10s and smoothed the turbulence by a three-point window. Then the spectra is decomposed by fitting as Gaussian distribution. Using the decomposed spectra to study a stratocumulus. The air motion is estimated by treating the small cloud particles as the tracer of air motion. The microphysical properties are retrieved by means of the Frisch model.