Study On The Distributions And Physical Properties Of Cirrus Clouds

Cirrus clouds play an important role in atmospheric radiation, its horizontal distributions influence to the radiation field of earth and atmosphery system, and the parameters in vertical direction have a feedback effect on climate, which is also very important. In this paper, cirrus horizatal distributions, optical properties and microphysical properties are studied using the data from artificial observation, micro-pulse lidar and the millimeter wave radar.(1) The characteristics such as horizontal distributions and seasonal variations of cirrus are analyzed using the hourly cloud form data at756observation stations in China region during the period from the time in which the observations are set up to December in2010. The results show that the occurrence frequncy of cirrus spissatus is higher than the other three kinds of cirrus and high in north and low in south, also the highest values appear in northweat of China and lowest values appear in southeast Sichuan. Additional, the occurrence frequncy have obvious seasonal variations. From winter to summer, the occurrence frequncy of cirrus continues to increases, But it reduces from summer to autumn.(2) By using cirrus measurements with a Micro Pulse Lidar at Beijing from November in2011to May in2012, the statistical analysis is made for cirrus height and thickness and optical depth is caculate. The results show that cirrus base height varies between5and10km,and the mean value is7.04±1.10km above sea level, cirrus thickness varies between0.3and1.5km, and the mean value is0.73±0.25km. cirrus optical depth is less than0.14. Cirrus cloud base height and thickness showed a negative correlation. Optical thickness and thickness were positively related.(3) A algorithm for retrievement of microphysical properties of cirrus based on micro-pulse lidar and millimeter wave radar is presented. In the algorithm, lidar extinction coefficient which is retrieved from backscatter signal intensity and water equivalent radar reflectivity factor are combined to obtain cirrus-cloud ice water content (IWC) and general effective size (Dge). A cirrus case in Shouxian was analysed using the algorithm. The results showed that, the IWC and Dge are10-3～10-1gm-3and1～200μm respectively, which were consistent with the empirical values. The IWC and Dge’s changes with time were in accordance with the evolutions of cirrus. The analysis results implied the feasibility of retrieving microphysical properties of cirrus from micro-pulse lidar and millimeter wave radar data.