江西地区层状暖云微物理结构特征及云雨自动转化阈值函数的研究

本文利用机载云粒子探测设备对2014年11月6日至12月25日期间在江西地区探测获得的7次暖云飞行个例资料，详细分析降水云和非降水云的微物理结构特征。云雨自动转化阈值函数（T）是描述云内碰并强度的重要微物理参量。我们发现T值在云内分布呈现云底较小，随着云内高度的增加T值逐渐增大，并且在云中部和上部达到最大值；研究还发现降水云的T值在0.6以上的频率远大于非降水云，表明降水云中的碰并过程更强，云滴更易通过凝结和碰并过程形成雨滴，符合暖云降水机制。降水云中云滴谱相对离散度（ε）和云滴数浓度（N_c）的负相关程度较非降水云更为显著，随着T的增大，二者的负相关程度增强；相比于云滴平均半径（r_a）的变化，云滴谱标准差（σ）的变化主导ε–N_c负相关程度的增强。

Study of the Microphysical Structural Characteristics and Cloud-Rain Autoconversion Threshold Function of Stratiform Warm Clouds in Jiangxi

This study analyzes the microphysical properties of precipitating and nonprecipitating warm clouds based on seven-flight cloud measurements from 6 November 2014 to 25 December 2014 in Jiangxi Province. The autoconversion threshold function (T) represents the probability of collision–coalescence process occurrence in clouds, which is critical for determining the initial time and intensity of precipitation. The authors found that, in general, T increases with height above the cloud base, with the maximum value occurring in the middle and upper parts of clouds. The occurrence frequency of T>0.6 in the precipitating clouds is larger than that in the nonprecipitating clouds, indicating a stronger collision–coalescence process and a greater probability of raindrops generated by the condensation and collision–coalescence processes in the precipitating clouds. There is a negative relationship between the relative dispersion of cloud droplet size distribution (ε) and the number concentration of cloud droplets (N_c), and this negative relationship becomes more evident with increasing T. Compared with the average radius of cloud droplets (r_a), the standard deviation of cloud droplet size distribution (σ) dominates the enhancement of the degree of the negative relationship between ε and N_c.