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，海洋从太空中看起来是深蓝色的，但当存在覆盖大片海洋表面的大片层积云时，海洋看起来明显更亮。这是海洋表面和云的辐射特性之间紧密耦合的表现。因此，控制粒子数量和性质以及海洋平流层积云性质的因素可能在全球辐射平衡中发挥重要作用。描述辐射和形成云滴的种子之间关系的链接量化得很差，提供了政府间气候变化专门委员会目前评估的最不确定的气候作用力。由气泡破裂和被风从波顶撕裂的水雾产生的海水水滴蒸发形成直径从100纳米以下到几微米的海雾颗粒。它们可以起到云凝结核(CCN)的作用，然后是云滴。云滴数密度(ND)在很大程度上取决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，云的反射率越高。对于给定的云水含量，较高的ND会导致较小的平均液滴尺寸。在降雨开始前，含有较多小液滴的云层比含有较少大液滴的云层持续时间更长。这两种影响都会改变到达地表的辐射量以及对区域和全球地表温度的影响。海洋CCN数受海面初级颗粒通量的影响较大。产生的气溶胶的大小和数量因风速、波浪状态等条件的不同而有很大不同。大小和组成决定了生长的液滴的表面张力和化学活性，这是决定气溶胶粒子是否会形成云滴的关键参数。此前，海雾颗粒被认为是由类似于散装海水的无机盐组成，主要是氯化钠。然而，具有极强疏水性的生物碎屑可能会分配到海洋表面形成一层膜，最近的研究表明，在海洋大气中占主导地位的100 nm至1微米之间的颗粒含有丰富的来自该海面微层的有机物质。英国SOLAS资助了三个项目，这些项目正在调查海洋大气中CCN的形成和控制方面。SENAW和ACMME是试验性方案，旨在分别量化海洋CCN的通量和性质。GLOMAP气溶胶模拟项目旨在量化海洋CCN的影响。建议利用资助的项目，通过在项目之间转让知识，以及巩固和扩大与国家、欧盟和更广泛的国际伙伴的合作，来增加综合产出。将与大量已确定的合作者一起举办一次初步研讨会，以探索最佳机制，以增进我们对控制CCN生产、性质和影响的各种工艺的作用的了解。合作者已经积极参与海洋CCN方面的研究，在所有情况下，资助的研究之间都存在显着的协同作用。其专长从直接测量海绵通量，到测量海洋气溶胶特性和详细识别有机成分，无所不包。所有方案都有重叠的利益，但具有显著的独特优势，因此可以充分探索从个别项目无法获得的联合科学发现。这些问题将在初次会议中进行探讨，并在随后的较小规模的交流中采取后续行动。将开展的一项已确定的知识转让活动是汇编和审查现有的海洋CCN数据，直接加强衡量项目和全球建模所需的评价数据。

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.