水云增长过程中的云滴谱及散射特性分析

基于大气物理学研究了水云云滴增长过程中的粒谱及散射特性.研究结果表明,凝结增长使粒谱半高宽和有效半径不断增加,碰并增长使粒谱出现多峰分布,有效半径增加.在凝结增长和碰并增长共同作用下,有效半径的平均增长速率为8 nm/s.凝结增长和碰并增长单独作用下,消光系数和散射系数随时间呈线性变化.在二者共同作用下,除3.2 mm波长外,消光系数和散射系数随时间呈指数增长;1.064, 2.2, 3.7, 12和22μm波长的不对称因子逐渐趋于稳定,200μm的不对称因子呈指数增长,3.2 mm的不对称因子基本保持不变;1.064和2.2μm波长的雷达比在20 sr附近波动,3.7μm波长的雷达比呈大幅振荡.云滴增长过程中,水云在1.064, 2.2和3.7μm波长的单次散射反照率逐渐降低,在12μm, 22μm, 200μm和3.2 mm波长的单次散射反照率逐渐增加,波长指数的绝对值逐渐减小.研究结果可为天气预报、地气辐射平衡研究和遥感数据校正提供重要的参考.

Analysis of particle size distribution and scattering characteristics of water cloud in condensation and coalescence growth

Study of scattering characteristics of water cloud is of great significance for weather forecasting, meteorological disaster warning, weather modification and research of radiation transmission in the lower atmosphere. In this paper, particle size distribution and scattering characteristics of water cloud in condensation and coalescence growth are studied by numerical simulation. The particle size distribution model of water cloud in the condensation growth and coalescence growth are established respectively. The dynamic process of the particle size distribution of water cloud in the condensation growth, the coalescence growth and the condensation-coalescence combination growth are analyzed. Then the scattering characteristics of water cloud in the droplet growth are studied with the Mie theory. The results show that with the condensation growing the full width at half maximum of particle size distribution, the effective radius and mode radius of water cloud increase continuously. The effective radius increases in the coalescence growth process and there are multiple peaks in the particle size distribution in the coalescence growth anaphase. The average growth rate of the effective radius of cloud droplets is 8 nm/s in the condensation-coalescence combination growth. The extinction coefficient and scattering coefficient of water cloud increase linearly with time increasing during the condensation growth or the coalescence growth. In the condensation-coalescence combination growth, the extinction coefficient and scattering coefficient increase exponentially with time increasing except at a wavelength of 3.2 mm; the asymmetric factors at the wavelengths of 1.064, 2.2, 3.7, 12 and 22 μm tend to be stable, while the asymmetric factor at the wavelength of 3.2 mm remains the same basically. Meanwhile, the lidar ratio at each of the wavelengths of 1.064 μm and 2.2 μm fluctuates near 20 sr, and that at the wavelength of 3.7 μm fluctuates greatly. In the growth process of cloud droplet, the single scattering albedo of water cloud decreases gradually at each of the wavelengths of 1.064, 2.2 and 3.7 μm, while it increases gradually at each of the wavelengths of 12, 22, 200 and 3.2 mm. The absolute value of Ångström exponent decreases gradually, which means that the wavelength-dependence of extinction coefficient decreases with cloud droplet growing. These research results reveal the change law of particle size distribution and the scattering characteristics of water cloud in condensation and coalescence growth. The results provide important reference for forecasting weather, studying earth-atmosphere radiation balance and correcting remote sensing data.