Retrieval of ice cloud microphysical properties at the SACOL

Abstract

Ice clouds are one of the most widely distributed cloud types in the world and play an important role in the radiation budget. The microphysical parameters of ice clouds, such as ice water content, effective radius and particle concentration, have a significant effect on the artificial influences on weather, the calculation of the radiation effect and climate feedback of ice clouds. Because of their unique physical and optical properties, ice clouds play an important and unique role in the radiation budget. Understanding and recognizing the microphysical properties of ice clouds are of great significance for studying the effects of ice clouds on climate change. Ka-band zenith radar (KAZR), which has been deployed at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) since July 2013, has continuously operated for many years. By using the observation data from KAZR and micropulse lidar (MPL), we compare the microphysical properties of ice clouds, including ice effective particle size (Dge) and ice water content (IWC), which were derived from three algorithms: a traditional algorithm (Microbase), the Z-IWC-T relationship algorithm (Hogan) and the KAZR-MPL retrieval algorithm (Combined). Then, we compute and examine the radiative fluxes using each set of cloud properties as inputs to a radiative transfer model and compare the top-of-atmosphere (TOA) radiative fluxes to the satellite measurements to assess the impact of the differences in the microphysical quantities of different ice clouds on radiation. Our analysis shows that ice clouds mainly appear from 2 to 14 km and peak by approximately 13.02% at 7 km. The ice water contents retrieved from the three different inversion methods show a unimodal distribution. The ice water content is mainly concentrated in the range of 0.01−10 mg/m3, and the corresponding maximum probability of ice water content is concentrated in the vicinity of 0.1 mg/m3. However, there are some differences between the degrees of data concentration and the peak probabilities of the different algorithms. The effective particle size distributions obtained by the three methods are quite different. The effective particle size of the ice crystal inversion by the Microbase algorithm is unimodal, and the data are mainly concentrated in the small particle radius region of 0−100 μm. The KAZR-MPL algorithm has a wider range of particle distributions, with two peaks at 40 and 96 μm. However, the distribution of the ice effective particle radius shows significant discrepancies, which sometimes translate into large differences in the cloud shortwave radiative effect. Using the results of three different microphysical properties, the longwave and shortwave radiation fluxes at the top of the atmosphere are calculated through the Fu-Liou radiation transfer model. The results show that the longwave radiation fluxes calculated by using different cloud microphysical characteristics are in good agreement with the satellite observation data. The average error is 5.04%, and the correlation coefficients are all greater than 0.6. Compared with the observed longwave radiation, the Hogan algorithm that considers the temperature effect has a better simulation effect, the correlation coefficient is larger, and the root mean square error is smaller. The shortwave radiation is smaller than the observed values in the case of clouds, and the maximum error reaches 24.61%. The shortwave radiation flux simulated by the traditional empirical algorithm is closest to the satellite observations, and its root mean square error is significantly reduced compared with that of the other methods.