Aerosol-Cloud Coupling And Climate Interactions in the Arctic

北极的气候变化速度几乎比地球上任何其他地方都快，变暖速度是全球平均水平的两倍。这种变暖伴随着海冰的迅速融化--2007年夏季冰面积创历史最低纪录，此后几年夏季冰面积分别为有记录以来第二和第三低--并且海冰逐年变薄。北极地区的强烈变暖是由于几个正反馈过程造成的，包括海冰反射率反馈（温暖的条件会融化冰，降低混合冰/海洋表面的平均反射率，从而吸收更多的太阳辐射，导致冰融化增加并进一步降低）。反射率）和几个云反馈。在地球仪的大部分地区，低云的作用是使表面变冷，因为它们反射太阳光;在北极地区，高反射率的冰层表面降低了云反射率的重要性，而云水水滴对红外辐射的吸收成为主要影响--这将热量截留在云下，使表面变暖。尽管气候模型通常显示北极地区存在强烈的温室效应，它们在北极的分歧也比其他任何地方都大，从而产生了更广泛的未来气候条件。这些模型也往往不能非常准确地再现当前的北极气候条件。北极气候模型中的这种巨大不确定性主要是由于模型中物理过程的代表性差，以及一些独特和特别具有挑战性的条件。最大的不确定性来源是云的表示。这些模型使用的是从中纬度或热带云系的观测中得出的云特性的简单表示--这些云系的条件与北极地区的条件非常不同。该项目将对云的微物理特性、边界层的垂直结构和气溶胶特性以及云上、云下和云内的太阳和红外辐射通量进行空中现场测量。它还将测量表面气溶胶的产生率和特性及其随季节和海冰覆盖范围的变化。将使用这些测量结果，沿着一系列气溶胶和云过程的数值模型以及大气动力学，以评价海冰范围、气溶胶产生和云特性之间的相互作用。将在MetOffice气候模型HadGEM中开发、测试和实施适用于气候模型的新的和改进的描述。我们将测试当前MetOffice模式再现观测到的北极云和边界层特性的能力，并评估新参数化方案的影响。最后，我们将进行一系列气候模拟，以研究未来气候将如何演变，以及北极变暖、海冰融化、气溶胶产生和云特性之间的反馈。

The climate of the Arctic is changing faster than that almost anywhere else on Earth, warming at a rate of twice the global average. This warming is accompanied by a rapid melting of the sea ice - 2007 saw a record minimum in summer ice extent, and the years since have seen the 2nd and 3rd lowest summer ice extents on record - and a thinning of the ice that remains from year to year. The strong warming in the Arctic is due to several positive feedback processes, including a sea-ice albedo feedback (warmer conditions melt ice, lowering the average reflectivity of the mixed ice/ocean surface and thus absorbing more solar radiation, leading to increased ice melt and further lowering of the albedo) and several cloud feedbacks. Over most of the globe low clouds act to cool the surface since they reflect sunlight; over the arctic the highly reflective ice surface reduces the significance of cloud reflectivity, and the absorption of infrared radiation by cloud water droplets becomes the dominant effect - this acts to trap heat below cloud, warming the surface.Although climate models generally show a strong greenhouse warming effect in the Arctic, they also disagree with each other more in the Arctic than anywhere else, producing a wider range of possible future climate conditions. The models also tend not to be able to reproduce current Arctic climate conditions very accurately. This large uncertainty in models of the Arctic climate results primarily from poor representation of physical processes within the models, and some unique and particularly challenging conditions. The largest single source of uncertainty is the representation of clouds. The models use simple representations of cloud properties that were developed from observations in mid latitude or tropical cloud systems - very different conditions from those that exist in the Arctic. This project will make airborne in situ measurements of cloud microphysical properties, the vertical structure of the boundary layer and aerosol properties, and the fluxes of solar and infra red radiation above, below, and within cloud. It will also measure the production rates and properties of aerosol at the surface and their variability with season and extent of sea ice cover. These measurements will be used, along with a range of numerical models of aerosol and cloud processes, and atmospheric dynamics to evaluate the interactions between sea ice extent, aerosol production and cloud properties. New and improved descriptions of these processes suitable for use within climate models will be developed, tested, and implemented within the MetOffice climate model HadGEM. The ability of the current MetOffice models to reproduce the observed Arctic cloud and boundary layer properties will be tested, and the impact of the new parameterization schemes evaluated.Finally we will undertake a series of climate simulations to examine how future climate will evolve, and the feedbacks between warming of the Arctic, melting of sea ice, production of aerosol, and the properties of clouds evaluated.