Atmospheric ice nuclei in the Arctic

北极气候变化的速度是全球平均速度的两倍，这些巨大的变化在过去几十年中海冰范围的减少中显而易见。2007年记录了迄今为止最低的海冰覆盖率，最近的数据表明今年的海冰覆盖率可能更低。云在北极气候中起着重要作用，因此影响着海冰的范围，但我们对这些云的了解非常少。在世界大部分地区，低层、视觉上厚的云往往有冷却效果，因为它们将阳光反射回太空，否则这些阳光将在表面被吸收。然而，在北极地区，这一影响并不那么重要，因为北极的表面通常被冰雪覆盖，已经具有高度的反射性，因此北极的云层往往会变暖而不是变冷。反过来，北极的变暖会导致海冰破裂，暴露出黑暗的底层海水。海水吸收了更多的太阳能量，从而放大了最初的变暖。因此，云的性质或覆盖范围的微小变化可能导致北极气候的巨大变化;这就是拟议的研究项目的用武之地。很大一部分云，包括在北极地区发现的云，被归类为混合相云。这意味着它们包含过冷水滴和冰晶（有关过冷水的演示，请参阅：http://www.youtube.com/watch? v= 0JtBZGXd5Z0）。液态云滴可以在远低于零摄氏度的过冷状态下存在而不冻结。然而，如果液滴中含有一种称为冰核的颗粒，可以催化冰的形成和生长，那么就会观察到冻结。冰的形成会极大地改变云的性质，从而改变其对气候的影响。在低纬度地区，冰核通常由沙漠尘埃、煤烟甚至细菌组成。但北极环境中冰核的组成和来源仍然是一个谜。北极冰核的一个可能来源是海洋。在海面上，通过波浪破碎和气泡破裂的作用而排放的粒子，当它们被抛到大气中并被合并在云滴中时，可能会成为冰核。这种冰核的来源还没有被量化。我们将是第一个在北极中部地区测量冰核的人。我们将从一艘研究船上测量海洋表层的冰核，并从BAe-146研究飞机上测量空气中的冰核。海洋表面含有各种细菌、病毒、浮游生物和其他物质，这些物质被喷射到大气中，可能导致冰的形成。我们将使用在利兹开发的最先进的设备来测量来自海洋的颗粒和在大气中采样的颗粒如何成核冰。我们将依托NERC资助的一个名为ACACCIA的项目，该项目不仅物有所值（因为船只和飞机已经在ACCACIA下支付），而且是进入这一偏远地区的独特机会。拟议研究的结果将建立在默里实验室以前的工作基础上，并产生可直接用于改进基于计算机的云、气溶胶和气候模型的定量结果。我们的研究结果将进一步加深我们对这些神秘而重要的混合相云以及全球气候的理解。

The Arctic climate is changing twice as fast as the global average and these dramatic changes are evident in the decreases in sea ice extent over the last few decades. The lowest sea ice cover to date was recorded in 2007 and recent data suggests sea ice cover this year may be even lower. Clouds play a major role in the Arctic climate and therefore influence the extent of sea ice, but our understanding of these clouds is very poor. Low level, visually thick, clouds in much of the world tend to have a cooling effect, because they reflect sunlight back into space that would otherwise be absorbed at the surface. However, in the Arctic this albedo effect is not as important because the surface, often being covered in snow and ice, is already highly reflective and Arctic clouds therefore tend to warm instead of cooling. Warming in the Arctic can, in turn, lead to sea ice break-up which exposes dark underlying sea water. The sea water absorbs more of the sun's energy, thus amplifying the original warming. Hence, small changes in cloud properties or coverage can lead to dramatic changes in the Arctic climate; this is where the proposed research project comes in. A large portion of clouds, including those found in the Arctic region, are categorized as mixed phase clouds. This means they contain both supercooled water droplets and ice crystals (for a demonstration of supercooled water see: http://www.youtube.com/watch?v=0JtBZGXd5zo). Liquid cloud droplets can exist in a supercooled state well below zero degrees centigrade without freezing. Freezing will, however, be observed if the droplets contain a particle known as an ice nucleus that can catalyze ice formation and growth. Ice formation dramatically alters a cloud's properties and therefore its influence on climate. At lower latitudes, ice nuclei are typically made up of desert dusts, soot or even bacteria. But the composition and source of ice nuclei in the Arctic environment remains a mystery. A likely source of ice nuclei in the Arctic is the ocean. Particles emitted at the sea surface, through the action of waves breaking and bubble bursting, may serve as ice nuclei when they are lofted into the atmosphere and are incorporated in cloud droplets. This source of ice nuclei has not yet been quantified. We will be the first to make measurements of ice nuclei in the central Arctic region. We will make measurements of ice nuclei in the surface layers of the sea from a research ship as well as measuring airborne ice nuclei from the BAe-146 research aircraft.The sea's surface contains a wide range of bacteria, viruses, plankton and other materials which are ejected into the atmosphere and may cause ice to form. We will use state-of-the-art equipment developed at Leeds to measure how well sea-derived particles and particles sampled in the atmosphere nucleate ice. We will piggy back on a NERC funded project called ACACCIA, which not only represents excellent value for money (since the ship and aircraft are already paid for under ACCACIA), but is a unique opportunity to access this remote region. Results from the proposed study will build upon previous work performed in the Murray laboratory and generate quantitative results that can be directly used to improve computer-based cloud, aerosol and climate models. Our results will further our understanding of these mysterious and important mixed phase clouds and, in turn, the global climate.