Abstract:
The distribution properties of hydrometeor classification and supercooled liquid water content in clouds have important roles in clarifying the microphysical formation mechanisms of clouds and precipitation, as well as establishing and validating cloud microphysical parameterization schemes in numerical models. On basis of Ka?band radar data collected during the Second Tibet Plateau Scientific Expedition in Nyingchi, southeast Tibet Plateau, the distribution properties of hydrometeor classification and supercooled liquid water content for a typical precipitating stratiform cloud on September 16?17, 2019 are investigated after data quality control procedures. The results show that the data denoising rate of the cloud radar based on the “K?nearest neighbor frequency method” is within the range of 1.5 -5.0 %, and the data gap filling rate is within the range of 3.5-7.0%. The difference between the attenuation?corrected radar data and raw data is between 0 and 5 dBZ by applying an iterative correction method. It is found that the precipitation formation mechanism for the typical stratiform cloud in the study region had some unique characteristics. The precipitation was formed by the merging of middle and high clouds induced by lifting of large-scale atmospheric circulation with low?level clouds formed by orographic lifting. In the initial stage, cloud top reached 12 km and the clouds at upper and lower levels were separated distinctly. There was no evident bright band at the melting layer. The particle distribution within the cloud was relatively homogeneous, and ice crystals and snow particles were dominate with a relatively high supercooled liquid water content in the middle and high clouds. In the mature stage, the middle and high clouds merged with the low clouds, leading to precipitation formation and cloud top decrease to be around 10 km. The clouds became inhomogeneous with evident bright band at the melting layer and weak embedded convective cells. The dominant hydrometeors were ice and snow particles, with a small amount of graupel in the embedded convective cells. The supercooled liquid water content was mainly distributed in the embedded convective cells with a maximum value of 0.5?0.6 g m-3. In the decaying stage, as the large?scale weather system passed over the study region, the middle and high cold clouds weakened rapidly, and weak warm rain generated by low?level orographic clouds became dominant, resulting in the disappearance of the bright band at the melting layer. A thin layer of ice and snow was present above the melting layer.