【摘要】 雨滴下落过程是云降水物理研究中极为重要的一个部分,其研究涉及到蒸发过程和雨滴末速度问题。在静止大气中,对于单个云滴,Maxwell理论给出了粒子在凝结过程中的质量增长公式,而本文研究雨滴的下落过程,是与凝结过程相反的蒸发过程。基于Maxwell理论,将雨滴假定为球形粒子,对原方程进行差分求解,并加入通风效应与表面效应对Maxwell理论就行修正。在雨滴末速度问题上,本文采用2015年昆明站的探空资料,将雨滴直径(>1μm)分为三个部分,在忽略了雨滴短暂的加速过程后,考虑拖曳力F_D与重力F_g平衡进行讨论,用最小二乘法拟合得出初始高度的末速度与半径的关系,再结合部分假设和理论推导得到任意高度的末速度与半径的函数关系。最后,利用该模型,针对相对湿度做了敏感性实验,发现雨滴所处环境的相对湿度变小会明显加快小雨滴的蒸发。本文基于Maxwell理论等前人研究,加入部分假设得到了一个较为合理的包含了蒸发过程的雨滴下落模型,对还原真实大气中雨滴的下落过程有一定参考价值。更多还原

【Abstract】 As an essential part of physical process on cloud and precipitation,the falling process of raindrops is mainly related to evaporation and raindrop fallspeed.For a single cloud droplet in the stationary atmosphere,Maxwell’s theory produces the mass growth formula of particles during the condensation process.In this study,the falling process of raindrops focuses on the evaporation process rather than the condensation process.Based on Maxwell’s theory,raindrops are assumed to be spherical particles,to produce its drop process by solving the original equation solved with difference method,and modifying the Maxwell theory by adding effects of ventilation and surface.For the issue of raindrop fallspeed,using the sounding data of Kunming station in 2015,the raindrops sample are divided into three groups according to different diameter(>1 μm).Neglecting the short acceleration process of raindrops,the balance between drag force and the gravity is considered for discussion.The relationship between the fallspeed and radius at the initial height is obtained by fitting with the least square method.And then the functional relationship between the fallspeed and radius at any height is obtained by combining some assumptions and theoretical derivation.Finally,several sensitivity experiments on relative humidity are tested by using this model.The result shows that decreasing the ambient relative humidity will accelerate the evaporation of small raindrops.Based on Maxwell’s theory and other previous studies,this paper has obtained a more reasonable raindrop falling model by considering evaporation process through some assumptions,which is helpful to represent the realistic falling process of raindrops better.更多还原