Abstract: Ice clouds have a large impact on Earth’s hydrological systems and energy budget. The formation and growth processes of ice clouds are more complicated than those of water clouds and are not yet fully understood. To investigate the distribution of ice clouds in China and the factors affecting this distribution,this paper analyzes the horizontal and vertical distribution and seasonal variation of the fraction of heterogeneous ice clouds over China from January 2012 to December 2015. Heterogeneous ice clouds must have ice nuclei involved in their formation and formation temperatures greater than ?40° C. This paper uses the Cloud- Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) level- 3ice clouds data product (CAL_LID_L3_Ice_Cloud) to analyze the horizontal and vertical distribution of heterogeneous ice clouds over China from January 2012 to December 2015. Seasonal ice cloud variation is studied as well. Because of the thin optical depth and high altitude of ice clouds, aircraft and ground-based RSobservations are difficult. However, satellites are a useful tool for detecting ice clouds. In this study, China is divided southern and northern areas based on differences in the fraction of ice cloud distribution. The results of this study show that the differences in the fraction of ice clouds in northern and southern China are related to temperature, radiation, and ice nuclei from the ground. In northern China, the horizontal distribution of the fraction of ice clouds between ?40 and 0°C is approximately 30% higher than in southern China. The average height of ice clouds in southern China is higher than that in northern China; however,ice clouds in the north are closer to the ground and thus more affected by surface ice nuclei. The ice cloud formation process is promoted more in northern China than in southern China. Additionally, there is an obvious seasonal variation of the fraction of ice clouds. The difference between northern and southern China is large in winter but small in summer. A weak increased (approximately 5% ) fraction of ice clouds is observed in northern China in the cloud temperature bin that ranges from ?30 to ?10°C. In this temperature range, the contact and immersion freezing processes form ice particles. The results of this analysis indicate that these formation processes are promoted in the north. In the spring, autumn, and winter, the fraction of ice clouds in the north is higher than in the south. In summer, the fraction of ice clouds below ?8° C in the south exceeds that in the north. The fraction of ice cloud bins in the troposphere (below 10 km) was larger in northern China than in southern China andthe fraction of ice clouds between the north and the south shows a peak at around 6 km, about 50%. The fraction of ice clouds in northern and southern China was lowest in summer and highest in winter.

Key words: ice clouds, CALIPSO, regional differences