A satellite observation-based analysis of the distribution and formation mechanism of ice crystal number concentration over the Tibetan Plateau

Abstract. Cirrus clouds are located at the upper middle-lower troposphere and play an important role in the Earth's energy balance and the atmospheric water cycle. This study utilizes DARDAR-Nice data within June to August from 2006 to 2016 (except 2011), combined with CloudSat cloud products and other related aerosol products, to analyze the distribution characteristics and formation mechanisms of ice crystal number concentration (N_i) in cirrus clouds over the Tibetan Plateau (TP). The results indicate that N_i over the northern TP is significantly lower than that over the southern region, mainly due to differences in underlying aerosol concentration and the intensity of convective activity. Dominated by homogeneous nucleation, N_i exhibits a typical ‘V’ shaped vertical profile over the TP. When deep convective activity occurs, it facilitates the increase in N_i. In contrast, dust and smoke aerosols hinder the formation of N_i through heterogeneous nucleation.. Additionally, the vertical wind velocity near 400 hPa in the northern TP approaches zero, causing the N_i peak to appear prematurely below the homogeneous nucleation threshold temperature (-38 °C).