VAMOS Ocean-Cloud-Atmosphere-Land Study UK (VOCALS-UK)

低空云层覆盖了地球的很大一部分，并将大量的阳光反射回太空。因此，它们对地球的整体能源预算有着深远的影响。然而，尽管它们很重要，但在用于预测未来气候变化的气候模型中，它们的代表性仍然很差。人们普遍认为，这种失败在很大程度上导致了目前对未来全球变暖水平的不确定性。此外，我们现在知道，悬浮在大气中的小颗粒，即气溶胶，可以通过改变云滴的数量和大小来影响云反射阳光的效率。我们也知道水滴的数量和大小影响云的寿命和它产生降雨的能力。这些过程的量化仍然很差，不能以任何程度的确定性进行建模，但对于确定气候对温室气体增加的敏感性至关重要。地球上的某些地方特别有利于形成大面积的低层层积云。其中许多都出现在亚热带地区，那里的海洋空气被来自深海的上涌冷水冷却。南赤道太平洋（SEP）地区支持着世界上最大的半永久性云甲板之一，因为这里的海洋表面温度比任何其他同等纬度的地方都要低。有充分的证据表明，这些云不仅影响当地的热量收支，而且对更广泛的太平洋地区的大气和海洋环流也有深远的影响，包括厄尔尼诺现象。SEP地区也很有趣，因为它与安第斯山脉相连，这些山脉对风的控制很强。沿着安第斯山脉的大规模采矿活动，遍及秘鲁和智利，排放了大量的气溶胶。这些扰动了海洋云层的特性，并提供了一个独特的、天然的实验室，用于研究气溶胶与云沿着从海岸延伸出去的强污染梯度的相互作用。认识到这一地区的根本重要性，国际社会制定了一项计划，以前所未有的细节研究SEP气候系统。该研究被称为VOCALS （VAMOS海洋-云-大气-陆地研究），由世界气候研究计划的VAMOS（美国季风系统变异性）小组协调。VOCALS在2008年底进行了一项主要的野外实验，以调查气溶胶、云和南美海岸辐射场之间的相互作用，并利用船只和海洋浮标对海气耦合过程进行了广泛的测量。英国计划用其研究飞机参与其中，对海洋边界层的云和气溶胶特性进行详细测量。与此同时，将有一个协调一致的努力来检查气候模式如何很好地捕捉SEP地区的气候及其对更广泛的热带太平洋的影响。直到最近，这些模型还没有足够的空间分辨率，以一种现实的方式捕捉安第斯山脉、海洋上升流和涡流混合对海洋表面温度的影响，从而捕捉形成和维持层积云甲板的气象过程。英国在计算能力和高分辨率耦合气候模型方面的最新进展意味着这现在是可能的。该提案代表了英国对VOCALS的重大贡献，并汇集了以下领域的领先研究小组：全球气候和天气建模；气溶胶和云的机载测量及其辐射影响；一系列尺度上气溶胶和云特性的模拟。这项研究的结果将是对SEP气候有更深入的了解，从而改善气候模式中云、气溶胶和海洋过程的表征，并最终对未来气候做出更有信心的预测。

Low level clouds cover a substantial fraction of the Earth and act to reflect a significant amount of sunlight back to space. Thus they have a profound influence on the planet's overall energy budget. Despite their importance, however, they remain poorly represented in the climate models used to make predictions of future climate change, and it is generally agreed that this failure contributes substantially to the current uncertainties in future levels of global warming. Furthermore, we now know that small particles suspended in the atmosphere, known as aerosols, can affect how efficiently these clouds reflect sunlight, by changing the number and size of cloud droplets. We also know that the droplet number and size affects the cloud's lifetime and its ability to produce rainfall. These processes remain poorlyquantified and cannot be modeled with any degree of certainty, but are critically important for the determining how sensitive the climate will be to increasing greenhouse gases. Certain locations on the planet are particularly conducive to the formation of extensive sheets of low level, stratocumulus cloud. Many of these arise in the subtropics where marine air is cooled by upwelling cold water from the deep ocean. The Southern Equatorial Pacific (SEP) region supports one the largest semi-permanent cloud decks in the world due to the ocean surface temperatures being colder here than at any other equivalent latitude. There is good evidence that these clouds affect not only the local heat budget, but also have a profound effect on the atmosphere and ocean circulation over the wider Pacific region, including El Nino. The SEP region is also interesting because of its conjunction with the Andes and the strong steering of the winds that these mountains exert. Extensive mining activities along the Andes, throughout Peru and Chile, emit considerable amounts of aerosol. These perturb the properties of the marine cloud layer and provide a unique, natural laboratory for investigating aerosol-cloud interactions along a strong pollution gradient extending away from the coast. Recognising the fundamental importance of this region, the international community has developed a programme to study the SEP climate system in unprecedented detail. Called VOCALS (VAMOS Ocean-Cloud-Atmosphere-Land Study), it is coordinated by the VAMOS (Variability of the American MOnsoon Systems) panel of the World Climate Research Programme. VOCALS is conducting a major field experiment in late 2008 to investigate the interaction between aerosols, clouds and the radiation field off the South American coast, as well as making extensive measurements of air-sea coupling processes using ships and ocean buoys. The UK plans to participate with its research aircraft, making detailed measurements of cloud and aerosol properties in the marine boundary layer. At the same time there will be a concerted effort to examine how well climate models capture the climate of the SEP region and its impact on the wider tropical Pacific. Until recently, these models have not had sufficient spatial resolution to capture in a realistic way the effects of the Andes, of ocean upwelling and eddy mixing on ocean surface temperatures, and thereby the meteorological processes that form and maintain the stratocumulus deck. Recent advances in the UK in computing power and in high resolution coupled climate modeling have meant that this is now possible. This proposal represents a significant UK contribution to VOCALS and brings together leading research groups in the areas of: global climate and weather modeling; airborne measurements of aerosols and clouds and their radiative influence; modeling of aerosol and cloud properties on a range of scales. The outcome of this research will be a greater understanding of the SEP climate, leading to improved representations of clouds, aerosols and ocean processes in climate models and ultimately to more confident predictions of future climate.