关键词: 卫星探测, CloudSat, 垂直结构, 云, 江淮地区

Abstract: Objective　More than 50% of the Earth's surface is covered by clouds. Clouds play a crucial role in the Earth atmosphere system, serving as key regulators of the Earth's radiation balance and global water cycle. The characteristics of cloud vertical structure, including cloud water content, cloud water path, cloud top and base heights, and cloud thickness, reflect the internal dynamic and thermodynamic processes of clouds and the mechanisms of cloud precipitation microphysics, which have a significant influence on atmospheric radiation transfer. The uncertainty of cloud vertical structure remains one of the major obstacles to understanding the impact of clouds on climate. Therefore, an in depth understanding of cloud vertical structure is of great significance for further research on climate change. In this study, CloudSat satellite observation data were employed to analyze the vertical structure characteristics, as well as the macro- and micro-physical characteristics, of cloud systems over the Yangtze-Huaihe region during the Meiyu period, in order to deepen the understanding of cloud system features in this region. Methods　Based on the Level 2 product data from the Cloud Profile Radar (CPR) onboard the CloudSat satellite, the satellite transit orbit data during the Mei-yu period (mid-June to mid-July) from 2015 to 2019 over the Yangtze-Huaihe region (28°N–34°N, 110°E–122°E) were selected. During the study period, a total of 53,040 satellite profiles passed over the region. For each profile, the 2B-GEOPROF product was first used to determine whether there were clouds present at the subsatellite pixel. When there were clouds, the 2B-CLDCLASS product and 2B-CWC-RO would be used to analyze the macroand micro-physical parameters of clouds, including cloud layer distribution, cloud type, cloud top and cloud base heights, and cloud microphysical parameters (cloud water content, effective radius, number concentration). In addition, the microphysical characteristics of deep convective clouds and the precipitation features of different cloud layers were also analyzed. Results and Discussion　The macro- and micro-physical characteristics of clouds during the Mei-yu period in the Yangtze- Huaihe region were analyzed using CloudSat satellite product data from 2015 to 2019. The results indicate that single-layer clouds dominate in the Yangtze-Huaihe region during the Mei-yu period, accounting for 49.3%, followed by two-layer clouds, accounting for 33.7%. Cirrus clouds account for 34.5% of all cloud types, followed by high cumulus clouds, with high-level clouds being predominant overall. The primary precipitation-producing cloud systems are deep convective clouds and nimbostratus, accounting for 7.0% and 4.4%, respectively. The average liquid water content of the cloud system during the Mei-yu period is 383.2 mg/m3, decreasing with height below 3 km and in range of 5–9 km, while remaining relatively stable at approximately 400.0 mg/m3 in the 3–5 km height layer. The average ice water content is 90.2 mg/m3, exhibiting an increasing trend in the 4–9 km altitude range, with a high -value region occurring in the 7–11 km altitude range. The average effective radius of liquid water droplets is 15 μm, with values exceeding 12 μm accounting for 67.2% of the total samples, and decreasing with heights below 3 km. The average effective radius of ice crystals is 69 μm, with a maximum value of 101 μm observed at a height of 5.3 km. The average droplet concentration in water clouds is 55 cm−3, which decreases with height below 3 km and in the 5–9 km altitude range, and remains nearly constant at approximately 70 cm−3 in the 3–5 km height layer. The average droplet concentration in ice clouds generally increases with height. Around 31°N, the high proportion of deep convective clouds (15.2%) results in the development of deep clouds (with a mean cloud thickness of 5.2 km), and both the ice water content and ice cloud droplet concentration in the 14–16 km height layer are significantly higher than in other regions. The vertical structure of ice cloud particles in deep convective clouds is similar to that of all cloud systems, while exhibits higher values at each altitude and a more pronounced vertical variation trend. The precipitation frequencies for deep convective clouds, nimbostratus, and cumulus are 93.0%, 86.1%, and 68.1%, respectively. The precipitation in deep convective clouds and nimbostratus is primarily associated with single-layer clouds, whereas the precipitation in cumulus arises mainly from both single-layer and two-layer cloud systems. Conclusions　Based on the CloudSat satellite observations from 2015 to 2019, this study systematically investigates the vertical structural characteristics, macro- and micro-physical properties of cloud systems over the Yangtze – Huaihe region during the Meiyu period. These results provide an observational benchmark for understanding cloud vertical heterogeneity in this subtropical monsoon region and offer valuable constraints for evaluating cloud parameterizations in numerical models and improving satellite‑based precipitation retrieval algorithms.

Key words: satellite detection, CloudSat, vertical structure, cloud, Yangtze-Huaihe region