Classification of Cloud Phase Using Combined Ground-Based Polarization Lidar and Millimeter Cloud Radar Observations Over the Tibetan Plateau

The distributions of cloud phases play an important role in influencing the weather and climate system. The characteristics of clouds above the Tibetan Plateau (TP) can profoundly affect regional and global atmospheric circulation. To research the distributions of cloud phases in the TP region, a retrieval algorithm was developed based on the combination of polarization lidar and millimeter cloud radar measurements and applied to the data from a comprehensive field campaign on the central TP in the summer of 2014. The structure and phase of four different types of clouds were retrieved accordingly, which validates the reliability of the algorithm. The result shows that the occurrence frequency of low clouds remains around 50%, which is very high throughout the whole day in Nagqu, Tibetan in summer. The liquid and mixed cloud frequencies are higher in the morning and afternoon, while ice cloud mainly occurs from the afternoon to midnight. Liquid and ice phase distributions show an inverse relationship in the atmospheric layer from 2 to 8 km in height. Meanwhile, the proportion of the liquid phase to the cloud top is significantly higher than that to the cloud body, which indicates that the supercooled water is more likely to appear at the cloud top than in the cloud. The fractional probabilities of the ice phase and liquid phase in the total cloud top phase intersect at about
$-26.7\,\,^{\circ }\text{C}$
.