关于雨滴在云下蒸发的数值试验

THE NUMERICAL TEST ON EVAPORATION OF RAINDROP BENEATH CLOUD

摘要: 顾震潮1、Mason2、Twomey3、北京大学云物理教学组4、Kuhme5等均曾讨论过雨滴的蒸发问题。他们认为雨滴与环境的热交换随时达到平衡,未考虑雨滴蒸发消耗热量与环境向雨滴传导热量的补偿不平衡;以及雨滴在下落中保持高层较低温度的倾向(热滞后),从而造成的滴表面饱和水汽压保持在较低水平,抑制了蒸发的情况。本文通过对云下雨滴下落蒸发过程的数值试验,讨论了:①下落的雨滴由于蒸发消耗热量,温度比周围环境低,并有保持较高层次的较低温度的倾向。②在不饱和大气中的雨滴下落,由于雨滴温度低于环境温度,蒸发过程受到了抑制,甚至可能发生凝结过程。延长了雨滴在云下不饱和大气中下落的距离与存在时间,因而减小了最小可落地雨滴的尺度。

Abstract: In this paper, the evaporating process during the raindrops falling beneath cloud has been tested numerically. The main results show that(1)the temperature of falling drops is lower than that of surroundings because of the evaporation of raindrop heat, and also the falling drops tend to ramain the lower temperature of higher layer;(2) since the temperature of drops is lower than that of surroundings, the evaporating process during raindrop falling in unsaturated atmosphere is restrained, even the condensing process occurs possibly.