Optical Properties of Cirrus Transition Zones over China Detected by CALIOP

• Published in: Journal of Meteorological Research Vol. 31; no. 3; pp. 576 - 585
• Main Authors: Cai, Hongke, Fu, Yunfei, Chen, Quanliang, Feng, Xiao, Tie, Xin, Tao, Ranting, Xu, Kepiao
• Format: Journal Article
• Language: English
• Published: Beijing The Chinese Meteorological Society 01-06-2017; School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026%School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026%School of Atmospheric Science, Chengdu University of Information Technology/Plateau Atmospheric and Environment Laboratory of Sichuan Province, Chengdu 610225; School of Atmospheric Science, Chengdu University of Information Technology/Plateau Atmospheric and Environment Laboratory of Sichuan Province, Chengdu 610225
• Subjects: Atmospheric Protection/Air Quality Control/Air Pollution; Atmospheric Sciences; Earth and Environmental Science; Earth Sciences; Geophysics and Environmental Physics; Meteorology; Special Collection on Meteorology and Environment over the Tibetan Plateau and Adjacent Regions; cirrus; temperature; lidar; wind speed; transition zone
• ISSN: 2095-6037; 2198-0934
• DOI: 10.1007/s13351-017-6044-3

A transition zone near cirrus lateral boundaries can be detected by CALIOP （cloud-aerosol lidar with orthogonal polarization）. In the present study, for such transition zones over China, a number of optical properties, such as the backscatter coefficient and depolarization ratio, showed transitional characteristics between cirrus and clear sky. The stepped horizontal profile showed sharp changes in particle number and morphology between cirrus clouds and clear sky. The color ratio, however, was unable to show cirrus transition features because of the low signal-to-noise ratio. Typical ice particles presented a color ratio of 0.55-1.25 and a depolarization ratio of greater than 0.12, which were significantly higher than those of clear sky. Therefore, optical properties in transition took the form of stepwise hori- zontal profiles. The proportion of typical-featured particles also demonstrated a stepped horizontal profile similar to the optical characteristics, but the relationship between the proportion and the optical characteristics was not uniform in the cirrus clouds, transition zone, and clear sky. Therefore, the optical changes in the transition zone were caused by not only the change in particle concentration, but also the change in the particles themselves. The probability dens- ity distribution of the transition-zone widths showed a positive skewness distribution, and transition zones with widths of 3-5 km occurred most frequently. Overall, transition-zone width decreased with increasing temperature and increased with increasing vertical and horizontal wind speeds. This trend demonstrated independence with the direc- tion of the vertical and horizontal winds. These observations implied that the transitional features were caused by ma- terial exchange, such as entrainment and turbulent transport, near the cirrus lateral boundaries, and by the phase trans- formation of particles, such as sublimation.