A Study On Retrieving Cloud Microphysical Parameters From Millimeter-wave Radar Observations

The microphysical parameters of the cloud are the basis for in-depth study of cloud physics and radiation effects.In this paper,the layered cloud microphysical parameters are retrieved from the cloud echo data detected by the ground-based Ka-band millimeter-wave radar after attenuation correction.The paper also studies the algorithm of retrieval of water cloud and ice cloud parameters by using dual-frequency radar data,and discusses the sensitivity of the algorithm to the parameters of the droplet spectrum and particle shape.And the simulation data is used to test the effect of the dual-frequency retrieval algorithm.The main conclusions are as follows:?1?The higher the temperature/humidity,the greater the atmospheric attenuation coefficient.In the standard atmospheric state,the atmospheric absorption coefficients at 35 GHz,94 GHz,and 220 GHz in the near-surface atmospherere are 0.08 dB/km,0.35 dB?km^-1 and 2dB?km^-1,respectively.From the ground to 12 km height,the two-way path integral attenuation is 0.4 dB,1.3 dB and 6.2 dB,respectively.?2?The attenuation coefficient of the liquid droplets is below 2 dB?km^-1,and the attenuation coefficient of the ice cloud is about three orders of magnitude smaller than that of the water cloud.The attenuation of the electromagnetic waves of the Ka-band radar by the ice cloud is almost negligible.But the dielectric factor of ice is about 0.174,which is 5.3 times smaller than 0.93 in the radar constant,which makes the measured radar reflectivity factor weaker than the actual radar reflectivity factor by about 7 dB and may lead to the lack of cloud boundary.?3?The median diameter range of altostratus case is 29.94⁵8.55?m,the concentration of particles is mainly concentrated in 10⁵¹0⁸ m^-3,and the liquid water content ranges from0.00 to 1.50 g?m^-3.And the equivalent median diameter of cirrostratus case ranges from 30.00to 50.93?m,the particle concentration ranges from 10⁵ to 10⁷ m^-3,and the ice water content ranges from 10^-3 to 10^-2g?m^-3.The liquid?ice?water content distribution is consistent with the radar reflectivity factor distribution,and the large particle region corresponds to the spectral width high value region.?4?For ice clouds,DFR?the dual-frequency ratio?algorithms have significant advantages over DDV?the differential Doppler velocity?algorithms because the radar reflectivity factor difference dynamic range is greater in dual-frequency,and the average Doppler velocity difference between the two bands is smaller.DFR and DDV can independently retrive D₀ in water clouds.But in the high frequency band,DFR algorithms are very sensitive to attenuation of rain,cloud water and water vapor,while DDV algorithms are not affected by attenuation.In view of the difficulty of completely correcting the attenuation of the high frequency band,the DDV retrieval method of the water cloud is more direct and more accurate.