Modelling of Summertime Arctic Stratus

夏季北极层层建模

• 批准号: NE/F013094/1
• 金额: $ 8.4万
• 依托单位: University of Leeds
• 依托单位国家: 英国
• 项目类别: Training Grant
• 财政年份: 2008
• 资助国家: 英国
• 起止时间: 2008 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FF013094%2F1
• 关键词: Modelling; Summertime; Arctic; Stratus

The Arctic is a region of exceptional sensitivity to climate change: the observed rate of temperature increase is twice that of the rest of the world, and there is strong evidence for thinning and retreat of Arctic ice pack ice, which reached a record minimum during 2007. Although models agree that the Arctic will continue to have a strong response to increasing greenhouse gas concentrations, they also show much greater variability between models here than elsewhere, and fail even to reproduce current conditions adequately. The response of the Arctic to continued climate change is thus extremely uncertain. Model performance in the Arctic is poor in large part because the parameterizations used are derived from observations in mid-latitudes or the tropics; there are very few measurements within the Arctic, with the result that our understanding of the processes controlling local conditions: cloud dynamics and microphysics, radiative forcing, surface exchange, etc, is poor. This PhD project will study the dynamical and microphysical processes in summertime Arctic stratus clouds using the Met Office Large Eddy Model and a single column version of the Unified Model. The aims are to understand the interactions between the cloud dynamics and microphysics, radiative forcing, and surface coupling, with the ultimate objective of improving the representation of Arctic boundary layer clouds in climate models. The project will assess 1) how the dynamics of Arctic stratus differ from typical marine stratocumulus, 2) what the role of entrainment is in maintaining the cloud in the unique humidity structure of the Arctic lower atmosphere, 3) how the cloud responds to different sources of aerosol: from the surface or entrained from above, since it is currently unknown where the CCN required to maintain Arctic stratus derive from. Such studies are of paramount importance since Arctic stratus is the dominant controlling factor for the surface energy budget, and differ substantially from their mid-latitude counterparts; failure to adequately represent these clouds in climate models makes it impossible to properly simulate Arctic climate. The project is directly linked to a major International Polar Year (IPY) field study taking place in the central Arctic in summer 2008: the Arctic Summer Cloud-Ocean Study (ASCOS). The ASCOS programme has been organised to address the issues above from an observational stance, and will provide an extensive data set for this project to draw upon. Measurements of direct relevance to this study include: aerosol physics and chemistry, boundary layer mean and turbulence structure from the surface through cloud top, surface energy budget, radiative fluxes, and cloud properties - both remotely sensed by cloud radar, lidar, microwave radiometers, etc, and in-situ measurements from a NASA P3 research aircraft. The ASCOS observations provide both the basis for establishing initial conditions for the modelling studies, and a means of assessing the fidelity of the simulations. The modelling study will in turn enhance the observational study by allowing controlled tests of the relative importance of the various factors controlling the cloud properties. The link to ASCOS and the IPY make the project particularly timely, provides access to a unique data set, and adds significant value to current NERC funded research. This link also provides exceptional training opportunities through interaction with the many international collaborators, involvement in ASCOS and IPY workshops and international meetings on polar science following the IPY. The primary supervisor (Brooks) is PI on the UK contribution to ASCOS, and a member of the programme steering group. The supervision team has extensive experience of analysing observational data, integrating it into models, and undertaking detailed process studies; Met Office collaboration results from their strong interest in resolving the issue of Arctic stratus in the UM.

北极是一个对气候变化异常敏感的地区：观测到的气温上升速度是世界其他地区的两倍，并且有强有力的证据表明北极冰块正在变薄和消退，在2007年达到了历史最低水平。尽管模型一致认为北极将继续对不断增加的温室气体浓度做出强烈反应，但它们也显示出这里的模型之间的差异比其他地方大得多，甚至无法充分再现当前的条件。因此，北极对持续气候变化的反应极其不确定。北极地区的模型性能很差，很大程度上是因为所使用的参数化来自于中纬度地区或热带地区的观测；北极地区的测量非常少，因此我们对控制当地条件的过程（云动力学和微物理、辐射强迫、表面交换等）的了解很差。该博士项目将使用气象局大涡模型和统一模型的单柱版本研究夏季北极层云的动力学和微物理过程。目的是了解云动力学与微物理、辐射强迫和表面耦合之间的相互作用，最终目标是改善北极边界层云在气候模型中的表示。该项目将评估：1）北极层云的动态与典型的海洋层积云有何不同，2）夹带在维持北极低层大气独特的湿度结构中的云中的作用是什么，3）云如何响应不同来源的气溶胶：来自地表或从上方夹带的气溶胶，因为目前尚不清楚维持北极层云所需的CCN来自何处。此类研究至关重要，因为北极层层是地表能量预算的主要控制因素，并且与中纬度地区的层层有很大不同；未能在气候模型中充分代表这些云，就无法正确模拟北极气候。该项目与 2008 年夏季在北极中部进行的国际极地年 (IPY) 重大实地研究直接相关：北极夏季云海研究 (ASCOS)。 ASCOS 计划的组织目的是从观察的角度解决上述问题，并将为本项目提供广泛的数据集以供利用。与本研究直接相关的测量包括：气溶胶物理和化学、从表面到云顶的边界层平均和湍流结构、表面能量预算、辐射通量和云特性——均由云雷达、激光雷达、微波辐射计等遥感，以及 NASA P3 研究飞机的现场测量。 ASCOS 观测结果既提供了建立建模研究初始条件的基础，也提供了评估模拟保真度的方法。模型研究将通过对控制云特性的各种因素的相对重要性进行受控测试来增强观测研究。与 ASCOS 和 IPY 的链接使该项目特别及时，提供了对独特数据集的访问，并为当前 NERC 资助的研究增加了重要价值。这一联系还通过与许多国际合作者的互动、参与 ASCOS 和 IPY 研讨会以及 IPY 之后的极地科学国际会议提供了特殊的培训机会。主要主管 (Brooks) 是英国对 ASCOS 贡献的 PI，也是项目指导小组的成员。监督团队在分析观测数据、将其整合到模型以及进行详细过程研究方面拥有丰富的经验；气象局的合作源于他们对解决密歇根大学北极层层问题的强烈兴趣。