| Precipitation is influenced by many different microphysical processes.The study of the microphysical characteristics of precipitation not only plays a fundamental role in understanding the cloud’s physical process but is also important to the improvement of the parameterization of numerical models and satellite remote sensing applications.As a means of remote sensing,weather radar can be used to obtain the spatial distribution and variation of precipitation particles,which plays an important role in understanding the microphysical process of precipitation in the air.However,the detection capability of traditional single-band radar for precipitation features is insufficient,and it is difficult to accurately retrieve the microphysical characteristics of hydrometers in the air.Based on the difference of scattering characteristics of particles in different bands,the dual-frequency retrieve techniques can realize the accurate retrieval of microphysical characteristics of precipitation.In this paper,a set of quality control algorithms of multi-mode pulsed compression millimeter wave radar based on Doppler spectra is established,and the radar data product after quality control is generated.Based on Ka and C band vertically pointing radars,a dual-wavelength radar retrieve method of rainfall microphysical parameters distribution was carried out and used to analyze the stratiform precipitation process in South China.A conceptual model of stratiform precipitation under different microphysical processes was proposed.The main contents and conclusions of this paper are as follows:（1）For the ground clutter and range sidelobe caused by applying the pulse compression technique,a Doppler-spectra-based data processing framework to improve the data quality of a multi-mode pulse-compressed Ka/Ku radar system.Firstly,non-meteorological signal close to the ground was identified with enhanced Doppler spectral ratios between different observing modes.Then,for the Doppler spectrum affected by the range sidelobe due to the implementation of the pulse compression technique,the characteristics of the probability density distribution of the spectral power were used to identify the sidelobe artifacts.Finally,the Doppler spectra observations from different modes were merged via the shift-then-average approach.The new radar moment products were generated based on the merged Doppler spectrum data.The quantitative evaluation results show that an increase in the number of coherent accumulations leads to a significant underestimation of radar reflectivity and Doppler velocity in heavy rain.The radar high-order moment data product error is significantly reduced after quality control.Among them,the standard deviation of spectral width near the melting layer in the cloud model of Ku-band radar is reduced from 0.14 m s-1 to 0.05 m s-1,the standard deviation of skewness is reduced from 1.61 to 0.26,and the standard deviation of kurtosis is reduced from 11.64 to 1.32.（2）Through forward simulation of radar observations,a lookup table of the raindrop size distribution（DSD）characteristic and air vertical velocity based on Ka-band spectral width and dual-wavelength Doppler velocity difference is established,and the application range of Ka-C band and Ka-Ku band combination lookup table is analyzed.The ideal simulation based on measured DSD shows that the root-mean-square error of the proposed method is 2.5 mm h-1,which is lower than that of the traditional reflectivity factor method(4.04 mm h-1).A precipitation event test of Ka and C band radar at Longmen Station in Guangdong Province shows that the retrieved rain rate is in good agreement with the measured results of surface DSD.By comparing the results of the Doppler spectra method with the Doppler velocity difference method,it is found that the power spectrum method is greatly affected by noise and air broadening.（3）C-band radar data were used to classify the precipitation in the Longmen observation station for two years.The results showed that the stratiform precipitation duration accounted for about 57.3%of the flood season precipitation time,and the stratiform precipitation in 2019contributed 44.26%of the accumulated rainfall in the flood season and 43.2%in 2020.The application of the Doppler velocity difference method to stratiform precipitation at Longmen Station in Guangdong reveals three stratiform precipitation types:evaporation dominant type,stable type and warm cloud growth type.The rain rate of the evaporation-oriented type decreases with the decrease in height,and the surface humidity in the 2-3 hours before precipitation occurs is usually lower than 80%.For the stable type,the rain rate does not change significantly with height,and the surface humidity before precipitation occurs is about 90%.The rain rate of warm cloud growth type increases with the decrease in height,and the surface humidity before rainfall is close to 100%.The retrieve results of air vertical velocity by dual-wavelength Doppler velocity difference method show that the air usually rises in the region with weak precipitation,which drives the elevation of the 0℃layer. |
