云光学厚度影响因子的模拟研究

Simulation Study on Influencing Factors of Cloud Optical Thickness

基于绝热气泡模式的模拟结果,研究了垂直速度、气溶胶数浓度和气溶胶的化学成分对云光学厚度的影响。模拟结果不仅能够很好地再现气溶胶第一间接辐射效应,且发现云光学厚度与垂直速度间的正相关性。当云中液态水含量不变时,垂直速度与气溶胶数浓度的增加导致云滴数浓度的增加和云滴有效半径的减小,进而使云滴总表面积增加、云的反照率增强。然而垂直速度与气溶胶数浓度的迅速增加导致云滴数浓度的增速与云滴有效半径的减速同时减缓,进而使云滴总表面积增速减缓、云的反照率增速减缓,云的光学厚度增速减缓。此外,当气溶胶数浓度粒径谱分布相同时,其化学成分分别为有机碳、硫酸铵、海盐时所对应形成云滴的有效半径依次减小、总表面积依次增加,所以云的光学厚度依次增加。该研究结果阐明了以上因素对云光学厚度的影响机理,有利于加深对气溶胶第一间接效应的理论认识。

Cloud optical thickness impacts the radiation balance of the earth–atmosphere system and is a key factor in climate change prediction.Furthermore,variation in cloud supersaturation predominantly relies on the physicochemical and activation characteristics of aerosols and the vertical velocity of updraft.These factors affect the activation process and condensation growth process within the cloud,ultimately changing the cloud optical thickness.Based on the simulation results of the adiabatic bubble model,the influences of vertical velocity,aerosol number concentration,and aerosol chemical composition on the cloud optical thickness were studied.The simulation results can reproduce the first indirect radiation effect of aerosols and show a positive correlation between cloud optical thickness and vertical velocity.When the liquid water content in the cloud remained constant,increasing the vertical velocity and aerosol number concentration increased the cloud droplet number concentration while reducing the cloud droplet effective radius.This phenomenon increased the total surface area of cloud droplets,ultimately enhancing the cloud albedo.However,with the rapid increase in vertical velocity and aerosol number concentration,the growth rate of cloud droplet number concentration and the cloud droplet effective radius slowed down simultaneously,consequently leading to a reduction in the growth rate of the cloud droplet total surface area,cloud albedo,and cloud optical thickness.Moreover,when the aerosol chemical composition comprises organic carbon,ammonium sulfate,and sea salt at the same aerosol number concentration,the cloud droplet effective radius decreases,leading to an increase in the total surface area and a consequent increase in the optical thickness of the cloud.The findings of this work have clarified the influence mechanism of the aforementioned factors on cloud optical thickness and deepened the theoretical understanding of the first indirect effects of aerosols.