Integration & Synthesis of Current Research into the Formation, Evolution and Roles of Cloud Condensation Nuclei in the Marine Environment

在没有云层覆盖的情况下，海洋从太空看是深蓝色的，但当大量的层积云覆盖了大片海洋表面时，海洋就明显变亮了。这是海洋表面与云的辐射特性之间紧密耦合的表现。因此，控制颗粒数量和性质以及海洋层积云性质的因素可能在全球辐射平衡中发挥重要作用。描述辐射与云滴形成的种子之间关系的链接很难量化，而且提供了IPCC目前评估的最不确定的气候强迫。气泡破裂和浪花被风从浪尖撕裂而产生的海水水滴蒸发后，形成直径从100纳米到几微米不等的浪花颗粒。这些可能作为云凝结核（CCN）和随后的云滴。云滴数浓度（Nd）高度依赖于进入云的粒子的数量、大小和组成。Nd反过来控制云的辐射特性，Nd越大，云的反射性越强。对于给定的云水含量，较高的Nd导致较小的平均液滴尺寸。含有较多小液滴的云比含有较少大液滴的云在下雨前持续的时间更长。这两种效应都会改变到达地表的辐射量，并对区域和全球地表温度产生影响。来自海面的初级颗粒通量将显著影响海洋CCN数。水滴的大小和数量，以及由此产生的气溶胶，随着风速、波浪状态等条件的变化而变化很大。大小和组成决定了生长液滴的表面张力和化学活性，这是决定气溶胶颗粒是否会形成云滴的关键参数。以前，人们认为海水喷雾颗粒是由无机盐组成的，类似于散装海水，主要是氯化钠。然而，具有明显疏水性的生物碎屑可能会在海洋表面形成一层薄膜，最近的研究表明，在海洋大气中占主导地位的粒径在100 nm至1微米之间的颗粒富含来自海洋表面微层的有机物质。英国SOLAS系统资助了三个项目，这些项目正在调查海洋大气中CCN形成和控制的各个方面。SEASAW和ACMME分别是旨在量化海洋CCN通量和性质的实验项目。GLOMAP气溶胶模拟项目旨在量化海洋CCN的影响。建议通过在项目之间转移知识，以及巩固和扩大与国家、欧盟和更广泛的国际伙伴的合作，利用资助项目来增加综合产出。最初的研讨会将与大量确定的合作者一起进行，以探索最佳机制，以提高我们对控制CCN生产，性质和影响的各种过程的作用的理解。合作者已经积极参与海洋CCN研究的各个方面，在所有情况下，受资助的研究之间都存在显著的协同作用。专业知识范围从直接测量海水通量，到测量海洋气溶胶特性和详细识别有机成分。所有的项目都有重叠的利益，但有显著的独特优势，因此可以充分探索共同的科学发现，这是单个项目无法实现的。这些问题将在首次会议上探讨，并在随后的小规模交流中予以跟进。一项确定的知识转移活动是汇编和审查现有的海洋CCN数据，为全球建模提供直接加强测量项目和必要的评估数据。

The oceans appears dark blue from space in the absence of cloud cover but appear significantly brighter when extensive sheets of stratocumulus clouds that cover large expanses of the ocean surface are present. This is a manifestation of the close coupling between the ocean surface and the radiative properties of clouds. Factors controlling the number and nature of the particles and in turn properties of the marine stratocumulus may thus play a major role in the global radiation balance. Links describing the relationships between radiation and the seeds upon which cloud droplets form are poorly quantified and provide the most uncertain forcings of climate currently assessed by the IPCC. Evaporation of seawater droplets generated by bubble bursting and spray torn from wave tops by wind form sea spray particles ranging from below 100 nm to several microns in diameter. These may act as cloud condensation nuclei (CCN) and subsequently cloud droplets. Cloud droplet number concentration (Nd) is highly dependent on number, size and composition of particles entering the cloud. Nd in turn controls the radiative properties of the cloud, the greater Nd, the more reflective the cloud. For a given cloud water content, higher Nd results in smaller average droplet size. Clouds comprising more small droplets last longer before onset of rain than those comprising fewer large droplets. Both effects change the amount of radiation reaching the surface and impact on regional and global surface temperatures. Marine CCN number will be significantly affected by the primary particle flux from the sea surface. The size and number of droplets, and hence aerosol, produced varies greatly with conditions: wind speed, wave state etc. Size and composition determine the surface tension and chemical activity of the growing drops, key parameters in determining whether an aerosol particle will form a cloud droplet. Previously, sea spray particles have been assumed to be composed of inorganic salts similar to bulk seawater, mainly sodium chloride. However, biological detritus which is significantly hydrophobic may partition to the ocean surface forming a film and recent work has shown that particles between 100 nm and 1 micron size dominating the particle number in the marine atmosphere are rich in organic material from this sea-surface microlayer. UK SOLAS has funded three projects which are investigating aspects of the formation and control of CCN in the marine atmosphere. SEASAW and ACMME are experimental programmes aiming to quantify the fluxes and properties of marine CCN respectively. The GLOMAP aerosol modelling project aims to quantify impacts of marine CCN. It is proposed to capitalise on the funded projects to increase combined outputs both by transferring knowledge between the projects and by consolidating and extending the collaboration with national, EU and broader international partners. An initial workshop will be conducted with a large number of identified collaborators to explore the optimum mechanisms for improving our understanding of the role of various processes controlling CCN production, properties and impacts. The collaborators are already actively engaged in aspects of research into marine CCN and significant synergy exists between the funded research in all cases. Expertise ranges from direct measurements of seaspray fluxes, through measurements of marine aerosol properties and detailed identification of organic components. All programmes have overlapping interests but significant unique advantages so allowing full exploration of joint scientific findings, inaccessible from individual projects. These will be explored in the initial meeting and followed up in subsequent smaller scale exchanges. One identified knowledge transfer activity to be conducted is the compilation and review of available marine CCN data, providing direct enhancement to the measurement projects and necessary evaluation data for global modelling.