Aerosol-Cloud Interaction - 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。由于人为和自然过程向大气中添加了气溶胶颗粒，云的性质可能会受到干扰。这一增加影响了云的微物理性质，随后影响了云的动力学和热力学，以及云与辐射相互作用的方式。地球的辐射预算受云层的影响非常大，而人类对影响云层的粒子负荷的变化，即所谓的间接影响，是巨大的和高度不确定的。这种不确定性在很大程度上是由于对基本气溶胶和云的性质和过程知之甚少，导致它们在模式中的表现不佳。这里提出了一项研究方案，以i)在实验室中直接调查这些过程，ii)评估气候相关参数对所研究过程的敏感性，iii)用详细的模式调查来解释实验室研究，以及iv)在云尺度和在可能的情况下，在全球尺度模式中纳入和测试对所研究过程的新描述。因此，该方案将减少估计与气溶胶和云过程有关的辐射强迫和气候反馈的不确定性。这些研究分为影响暖云的研究(只包含液体液滴的研究)和影响含有冰粒的云的研究。该方案汇集了一个跨学科的研究小组，这些研究人员具有“暖”和“冷”云和气溶胶过程方面的专门知识，将实验室和多尺度模拟活动结合起来，以提供改进的预测能力。“热”实验室的工作主要集中在两个方面：i)成长中的气溶胶粒子在成为云滴(或“激活”)时吸收水分的速率；ii)各种组成的气溶胶粒子作为云滴种子的能力。这些研究使用了许多技术，包括单粒子光学悬浮和在大型光化学室中进行的研究，以及对模拟大气化学过程中形成的粒子集合的大量化学和物理探测器。“冷”工作使用了大型、仪器齐全的云室实验和单粒子悬浮研究的类似耦合。用于这两个方面的舱室将耦合起来，利用来自两个舱室的仪器有效载荷，研究气溶胶转化条件对冷云和暖云形成的影响。将使用一系列详细的模型来明确描述气溶胶颗粒与增加相对湿度和降低温度相互作用形成云滴和冰晶的过程及其特性。这些过程和性质将在动力框架中表示，以预测气溶胶和云之间的相互作用及其在云分辨率尺度上的辐射效应，以及所研究的一些关于全球辐射强迫和反馈的性质的辐射强迫。气候相关参数对实验室方案中调查的基本参数及其改进的量化的敏感性将使用简化模型“模拟器”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'.