A case study of cirrus cloud over Wuhan city based on three-wavelength Raman-Mie lidar

To identify the optical characteristics of cirrus clouds and provide data support and scientific reference for atmospheric cloud detection research in Wuhan area, this study analyzed the optical parameter characteristics of convolutional cloud particles of a typical cirrus event in Wuhan in November 2023 based on the continuous observation data from a three-wavelength Raman-Mie lidar at Wuhan National Basic Meteorological Station from October to December 2023. The results are as follows. The average cloud base height of cirrus during this event was 7.0 km, and it showed a trend of slowly decreasing at night and gradually increasing during the daytime. During this period, the average lidar ratios at wavelengths of 355 nm and 532 nm were 40.6 Sr and 59.3 Sr, respectively. The phases of cirrus particles were identified by combining the backscattering coefficient and depolarization ratio. Small differences in backscattering coefficients across the three wavelengths at the cloud base and the cloud top were found, and the depolarization ratios were above 0.35, suggesting the dominance of non-spherical large particles during this event. However, the backscattering coefficients at wavelengths of 355 nm and 532 nm in the cloud were significantly higher than at 1064 nm with smaller depolarization ratios, indicating more spherical small particles in the cloud. The vertical structure of the cirrus showed an ice crystal-supercooled water-ice crystal distribution characteristic from the bottom to the top. The backscattering coefficient color ratios of both thinner and thicker cirrus clouds predominantly range from 0.5 to 0.8, with partial differences in the color ratio of 1064 nm and 355 nm wavelengths due to the influence of cloud thickness.