Study Of Cloud Microphysical Parameters Retrieval Based On Synergic Ground-Based Observation

High temporal and spatial resolution with long time series of cloud micro structure and macro characteristics can be obtained by employing millimeter wavelength cloud radar (MWCR). Microwave radiometer passively resolve the temperature and humidity profiles as well as cloud liquid water path in the atmosphere. Lidar is sensitive to small particles and capable of detecting cirrus fine structure. To study further the evolution of cloud microphysical parameters, and evaluate the detectability of different devices, a synergic observation of cloud by MWCR, microwave radiometer and lidar were performed. This paper carries out a preliminary study of stratus and cirrus microphysical parameters retrieval based on certain observation and experiment. The main work and conclusion are as follows:(1) Based on radar reflectivity factor, different single-factor methods were used to retrieval cloud liquid water content and cloud droplets effective radius through two light rainfall processes. Cloud occurrence showed on microwave radiometer products is corresponding to the height of wet layer. Cloud droplet effective radius is below 50 μm and raindrop radius is bigger up to 600 μm. By collision-coalescence process, cloud particles grow into raindrops. The precipitating cloud is of larger effective radius and less liquid water content.(2) Under the assumption of logarithm normal distribution of cloud size spectrum, fitted relationship was built up between reflectivity and liquid water path or stratus microphysical variables. Cloud droplets effective radius, number concentration and liquid water content were then calculated according to the fitted relationship. Comparative analysis showed the double-factor method has better adaptability. Before rainfall, the cloud microphysical variables fluctuated significantly with height, but the tendency became smooth after rainfall, which reflected that the cloud was getting more stable dynamically. Besides, the stratus cloud droplets concentration turned to be significantly less after rainfall.(3) Based on the assumptions of improved gamma distribution of cloud size spectrum and randomly oriented hexagons shape of ice crystals, a joint retrieval algorithm to estimate cirrus-cloud optical depth, ice water content (IWC) and general effective size (Dge) was presented. The range of Dge and IWC are between 10～ 90μm and 10-4～0.02g/m3 respectively. Cirrus optical depth lies in 0.1～2.5. Results show that a more continuous spatio-temporal distribution of cirrus microphysical characteristics can be obtained.