ASCOS Analysis - surface-cloud coupling in the arctic boundary layer

ASCOS 分析 - 北极边界层的地表-云耦合

• 批准号: NE/H02168X/1
• 负责人: Ian Brooks
• 金额: $ 41.44万
• 依托单位: University of Leeds
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2011
• 资助国家: 英国
• 起止时间: 2011 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FH02168X%2F1
• 关键词: ASCOS; Analysis; surface; cloud; coupling

The Arctic is a region of extreme sensitivity to climate change. Observations show its temperature to be increasing at twice the rate of the rest of the world. Models suggest this strong response will continue; however they also show a greater uncertainty here than for anywhere else in the world. The combination of rapid change and high uncertainty make improving predictive capability in the Arctic a matter of urgency. The strong climate response to increasing climate forcing by greenhouse gases is believed to be a result of several important feedback processes; for example the ice-albedo feedback, and several cloud-related feedbacks. Arctic stratus cloud is both extensive and long lived during the summer months. Their impact on the surface radiative budget, and hence on total energy budget, differs from that elsewhere in the world: sea ice and low clouds have very similar albedo, so that over ice the cloud has little impact on the solar radiation budget at the surface, and longwave (infra red) processes tend to dominate. Unlike anywhere else in the world, low cloud acts to warm the surface rather than cool it. The radiative properties of the clouds themselves also differ from lower latitudes because of different droplet size distributions. The Arctic has the lowest aerosol concentrations of anywhere on earth; a result of high deposition due to extensive cloud and fog, the great distance from strong continental aerosol sources, and the sea ice, which minimises marine sources. Aerosol provide the nuclei upon which cloud droplets form, so the low numbers mean the clouds have a smaller number of drops, which are consequently larger than typically found in mid-latitude stratus. The different drop-size distribution means Arctic stratus has different radiative properties than mid-latitude stratus: one of the reasons models represent their effects poorly. Small changes to cloud properties, whether from changes in aerosol availability, thermodynamic structure, or turbulent processes, can have a significant impact on their radiative properties. Small-scale processes must be parameterised in a simple form within climate models; these parameterisations must be based on measurement. Most measurements used have been from mid-latitudes or the tropics; thus the parameterizations derived from them are not necessarily appropriate for Arctic conditions. The difficulty and expense of making measurements in the Arctic has meant there are very few available against which to test the existing parameterisations or with which to develop new, more appropriate ones. The ASCOS field campaign achieved one of the most extensive and wide-ranging sets of measurements ever made in the central Arctic, and is intended to address the questions of what controls the properties of Arctic cloud. This proposal will use the unique ASCOS data set to study the interactions between the surface and the cloud that control the exchange of heat, water, and aerosol; and also the exchanges across cloud top with air from the free troposphere. It will study both the fundamental processes and examine how well they are represented within climate models, identify where parameterisations are failing, and propose alternative approaches more appropriate to the Arctic. The study will draw upon detailed in-situ and remote sensing measurements of lower-atmosphere structure, turbulent mixing, aerosol properties, cloud properties, and radiative fluxes to study the fundamental processes. These will be combined with large eddy simulation modelling to provide deeper insight into the 3-dimensional interactions, and allow perturbation experiments to be undertaken to study the relative importance of different parameters. Finally, the Met Office Unified Model will be used to study how parameterisations of these processes perform, and to discover weaknesses or failings within them. Ultimately this work will lead to improved parameterizations and more accurate predictions of future climate.

北极是对气候变化极其敏感的地区。观测显示，其气温上升速度是世界其他地区的两倍。模型表明这种强烈的反应将会持续下去；然而，与世界其他地方相比，这里也表现出更大的不确定性。快速变化和高度不确定性的结合使得提高北极的预测能力成为当务之急。人们认为，对温室气体气候强迫增加的强烈气候反应是几个重要反馈过程的结果；例如冰反照率反馈，以及一些与云相关的反馈。夏季，北极层云分布广泛且持续时间较长。它们对地表辐射预算以及总能量预算的影响与世界其他地方不同：海冰和低云具有非常相似的反照率，因此冰上云对地表太阳辐射预算的影响很小，长波（红外线）过程往往占主导地位。与世界其他地方不同，低云的作用是使地表变暖而不是使其冷却。由于液滴尺寸分布不同，云本身的辐射特性也与低纬度地区不同。北极地区的气溶胶浓度是地球上最低的；由于广泛的云雾、远离大陆强气溶胶源以及海冰而导致的高沉积量，从而最大限度地减少了海洋源。气溶胶提供了云滴形成的核心，因此较低的数量意味着云中的水滴数量较少，因此比中纬度层云中通常发现的水滴要大。不同的水滴尺寸分布意味着北极层层与中纬度层层具有不同的辐射特性：模型未能很好地体现其影响的原因之一。云性质的微小变化，无论是气溶胶可用性、热力学结构还是湍流过程的变化，都可能对其辐射性质产生重大影响。小规模过程必须在气候模型中以简单的形式参数化；这些参数化必须基于测量。大多数测量数据来自中纬度地区或热带地区。因此，从中得出的参数不一定适合北极条件。在北极进行测量的难度和费用意味着几乎没有可用的参数来测试现有的参数化或开发新的、更合适的参数化。 ASCOS 实地活动实现了北极中部有史以来最广泛和范围最广泛的测量之一，旨在解决控制北极云特性的问题。该提案将使用独特的 ASCOS 数据集来研究控制热量、水和气溶胶交换的地表和云之间的相互作用；以及云顶与自由对流层空气的交换。它将研究这两个基本过程，并检查它们在气候模型中的表现情况，确定参数化失败的地方，并提出更适合北极的替代方法。该研究将利用对低层大气结构、湍流混合、气溶胶特性、云特性和辐射通量的详细现场和遥感测量来研究基本过程。这些将与大涡模拟模型相结合，以更深入地了解 3 维相互作用，并允许进行扰动实验来研究不同参数的相对重要性。最后，英国气象局统一模型将用于研究这些过程的参数化如何执行，并发现其中的弱点或失败。最终，这项工作将改进参数化并更准确地预测未来气候。

项目成果

A transitioning Arctic surface energy budget: the impacts of solar zenith angle, surface albedo and cloud radiative forcing

北极地表能量收支的转变：太阳天顶角、地表反照率和云辐射强迫的影响

• DOI: http://dx.10.1007/s00382-010-0937-5
• 发表时间: 2010
• 期刊: Climate Dynamics
• 影响因子: 4.6
• 作者: Sedlar J

Cloud and boundary layer interactions over the Arctic sea ice in late summer

夏末北极海冰上云与边界层的相互作用

• DOI: 10.5194/acp-13-9379-2013
• 发表时间: 2013-09-24
• 期刊: Atmospheric Chemistry and Physics
• 影响因子: 6.3
• 作者: M. Shupe;P. Persson;I. Brooks;M. Tjernström;J. Sedlar;T. Mauritsen;S. Sjogren;C. Leck
• 通讯作者: C. Leck

Measurements of bubble size spectra within leads in the Arctic summer pack ice

北极夏季浮冰中铅内气泡尺寸光谱的测量

• DOI: http://dx.10.5194/os-7-129-2011
• 发表时间: 2011
• 期刊: Ocean Science
• 影响因子: 3.2
• 作者: Norris S

The Turbulent Structure of the Arctic Summer Boundary Layer During The Arctic Summer Cloud-Ocean Study

北极夏季云海研究中北极夏季边界层的湍流结构

• DOI: http://dx.10.1002/2017jd027234
• 发表时间: 2017
• 期刊: Atmospheres
• 作者: Brooks I

Evaluation of turbulent dissipation rate retrievals from Doppler cloud radar

多普勒云雷达湍流耗散率反演评估

• DOI: http://dx.10.5194/amtd-5-747-2012
• 发表时间: 2012
• 作者: Shupe M