A new approach for identifying dominant cloud types and relationships between cloud types and precipitation vertical structure in tropical regions

Cloud type profoundly affects precipitation, but few studies have explored its impact on precipitation scale height. The authors calculated the ratio of the volume of each cloud type to the total cloud volume and partitioned the tropical region based on the dominant cloud types. Based on this, tropical regions were categorized into altocumulus control regions, stratocumulus control regions, deep convective cloud control regions, and transition regions. These regions exhibit unique characteristics: high precipitation scale heights and low surface precipitation rates in altocumulus control regions; low precipitation scale heights and low surface precipitation rates in stratocumulus control regions; and moderate precipitation scale heights with high surface precipitation rates in deep convective cloud regions. These features arise from differences in cloud characteristics, precipitation probability, and intensity, influenced by varying water vapor structures. In terms of physical mechanisms, altocumulus, stratocumulus, and deep convective cloud regions are characterized by total dryness, upper-level dryness with lower-level wetness, and total wetness, respectively. Upper-layer dryness leads to low cloud and precipitation structures, reducing the precipitation scale height, while lower-layer dryness increases it. Different humidity conditions in the upper and lower layers lead to variations in cloud type and volume distribution, ultimately affecting precipitation scale heights. This finding aids the mechanistic study of cloud precipitation physics in the tropics, providing valuable insights for developing numerical models and parameterizations.

摘要

云类型对降水有重要影响, 但其对降水尺度高度的作用研究尚少. 本研究通过计算各云类型体积占总云体积的比例, 将热带地区划分为高积云, 层积云, 深对流云控制区及过渡区. 高积云区降水尺度高度较高, 地表降水率较低; 层积云区降水尺度高度和地表降水率均较低; 深对流云区降水尺度高度适中, 地表降水率较高. 这些特征由云特性, 降水概率和强度的差异决定, 并受到水汽结构的影响. 高积云, 层积云和深对流云区分别表现为整体干燥, 上层干燥且下层湿润, 以及整体湿润的特征. 上层干燥降低降水尺度高度, 下层干燥则升高高度. 上下层湿度差异影响云类型分布和降水结构, 最终决定降水尺度高度. 本研究为云降水物理机制研究及数值模式开发提供了新视角.