Aerosol-Cloud Interactions - A Directed Programme to Reduce Uncertainty in Forcing through a Targeted Laboratory and Modelling Programme

气溶胶粒子是云滴和冰粒形成的场所。人为和自然过程将气溶胶粒子加入大气层，可使云的特性受到干扰。这种添加影响云的微物理特性，并随后影响云的动力学和热力学，以及云与辐射相互作用的方式。地球的辐射收支受云的影响非常大，而人类引起的影响云的粒子负荷的变化，即所谓的间接影响，是巨大的，而且非常不确定。这种不确定性的很大一部分是由于对气溶胶和云的基本特性和过程缺乏了解，导致它们在模型中表现不佳。这里提出了一个研究方案，以i）直接在实验室中调查这些过程，ii）评估气候相关参数对所研究过程的敏感性，iii）用详细的模型调查解释实验室研究，iv）在云尺度和全球尺度模型中纳入和测试所研究过程的新描述。因此，该方案将减少与气溶胶和云过程有关的辐射强迫和气候反馈估计的不确定性。这些研究分为影响暖云（仅包含液滴）的研究和影响包含冰粒的云的研究。该计划汇集了一个跨学科的研究人员团队，他们具有“暖”和“冷”云和气溶胶过程的专业知识，结合实验室和多尺度建模活动，以提高预测能力。“暖”实验室工作集中在两个主要方面：i）当气溶胶颗粒变成云滴（或“激活”）时，水被增长的气溶胶颗粒吸收的速率; ii）各种成分的气溶胶颗粒作为云滴种子的能力。这些研究使用了一些技术，包括单粒子光学悬浮和调查，在一个大型的光化学室耦合到大量的化学和物理探针的粒子合奏在模拟大气化学过程中形成。“冷”工作使用了一个类似的耦合的大型，良好的仪器云室实验和单粒子悬浮研究。这两个方面所用的气室将结合起来，利用两个气室的仪器有效载荷，研究气溶胶转化条件对暖云和冷云形成的影响。将使用一系列详细的模型来明确地描述气溶胶粒子与增加的相对湿度和降低的温度相互作用形成云滴和冰晶的过程及其性质。这些过程和性质将在动力学框架中表示，以预测气溶胶和云之间的相互作用及其在云分辨尺度上的辐射效应，以及一些研究性质对全球辐射强迫和反馈的辐射强迫。气候相关参数对实验室方案中研究的基本参数的敏感性及其改进的量化将使用简化模型“仿真器”进行评估。

Aerosol particles act as sites for cloud droplet and ice particle formation. Cloud properties can be perturbed through the addition of aerosol particles into the atmosphere from anthropogenic and natural processes. This addition influences cloud microphysical properties, and subsequently affects cloud dynamics and thermodynamics, and the way the cloud interacts with radiation. The Earth's radiation budget is very greatly affected by clouds, and human-induced changes to the particle loading affecting them, known as indirect effects, are large and highly uncertain. A large part of this uncertainty is the result of poor knowledge of the fundamental aerosol and cloud properties and processes, leading to their poor representation in models. A programme of research is proposed here to i) directly investigate these processes in the laboratory, ii) evaluate the sensitivity of climate relevant parameters to the studied processes, iii) interpret the laboratory studies with detailed model investigations and iv) to incorporate and test new descriptions of the studied processes in cloud-scale and, where possible, global scale models. The programme will thereby reduce the uncertainty in estimates of radiative forcing and climate feedbacks relating to aerosol and cloud processes. The studies are split into those affecting warm clouds (those containing only liquid droplets) and those affecting clouds containing ice particles. The programme brings together an interdisciplinary team of researchers with expertise in 'warm' and 'cold' cloud and aerosol processes combining laboratory and multiscale modelling activities to deliver the improved predictive capability. The 'warm' laboratory work focuses on two major aspects i) the rate at which water is taken up by growing aerosol particles as they become cloud droplets (or 'activate) and ii) the ability of aerosol particles of various compositions to act as seeds for cloud droplets. These studies use a number of techniques including single particle optical levitation and investigations in a large photochemical chamber coupled to a large number of chemical and physical probes of ensembles of particles formed in simulated atmospheric chemical processes. The 'cold' work uses a similar coupling of a large, well-instrumented cloud chamber experiments and single particle levitation studies. The chambers used in both aspects will be coupled to investigate the impacts of aerosol transformation conditions on warm and cold cloud formation, using the instrumental payload from both chambers. A range of detailed models will be used to explicitly describe the processes by which aerosol particles interact with increasing relative humidity and reducing temperature to form cloud droplet and ice crystals and to their properties. The processes and properties will be represented in dynamical frameworks to predict the interactions between aerosols and clouds and their radiative effects at cloud resolving scales and radiative forcing of some of the investigated properties on global radiative forcing and feedbacks. The sensitivity of climate relevant parameters to the fundamental parameters investigated in the laboratory programme and their improved quantification will be evaluated using a simplified model 'emulator'.