Using Aircraft Observations and Modelling to Improve Understanding of Mineral Dust Transport and Deposition Processes

每年都有成千上万吨的矿物粉尘颗粒被强风从干旱地区吹起。在大气中，矿物粉尘对健康、运输和太阳能发电构成危害。尘埃通过与云、辐射和其他气溶胶相互作用，改变地球的能量平衡，从而影响气候。在北非和热带北大西洋等多尘地区，尘埃已被证明会影响西非季风和大西洋飓风的发展。尘埃在地球系统各组成部分之间形成了重要的联系和气候反馈：排放由陆地表面和大气因素驱动，同时通过空气传播影响大气，并通过沉积为海洋和陆地生物地球化学系统提供营养来源。几乎所有的粉尘过程都高度依赖于尺寸，而尺寸分布的真实表示对于模拟粉尘大气生命周期至关重要。然而，模型很难代表尘埃大小分布的演变。摩擦电荷和非球形等过程最近被认为是潜在的重要过程，但没有包括在尘埃模型中。这对沙尘模型准确反映沙尘对人类健康、基础设施、天气和气候影响的能力产生了连锁反应。直到最近，人们还没有观察到大的尘埃颗粒（10微米）。然而，在过去的十年中，飞机观测利用了新技术来测量尘埃的全尺寸范围，克服了以前测量的局限性。新的观测数据包括北非源附近的FENNEC，西大西洋的AER-D和东西大西洋的SALTRACE，提供了尘埃生命周期各个阶段的限制。本研究的目的是利用新的观测结果来研究沉积和输送过程对粉尘粒径分布的影响，从而提高我们对粉尘物理和微物理的理解。学生将在Met Office统一模型（UM）的框架内完成这项工作。提高对沙尘输送和沉积的认识将广泛适用，从而改善沙尘及其影响在气候模式中的表现。该奖学金由英国气象局的CASE赞助，并与美国国家科学院领导的北大西洋气候系统综合研究（ACSIS）项目相关联，因为沙尘输送在影响大西洋海面温度方面很重要。最初，观测数据将用于评估气候模式模拟中的尘埃。然后，通过依次禁用每个现有模式过程（如沉降、对流），以及引入新过程（如非球形和摩擦电荷的影响），可以评估各种过程对大西洋尘埃粒径分布演变的贡献。然后选择关键过程进行更详细的调查，使用UM或盒子模型，目的是了解大小偏差的原因并确定潜在的改进。最后，建议的发展将在全球气候时间尺度上进行测试。改进将直接适用于英国气象局的地球系统模型和数值天气预报模型。

Every year thousands of tonnes of mineral dust particles are uplifted from arid regions by strong winds. While in the atmosphere, mineral dust is a hazard for health, transport and solar energy generation. Dust affects climate by interacting with clouds, radiation and other aerosols and altering the Earth's energy balance. In dusty regions such as North Africa and the tropical North Atlantic, dust has been shown to influence the West African Monsoon and Atlantic hurricane development. Dust forms an important link and climate feedback between components of the Earth system: emissions are driven by land-surface and atmospheric factors, whilst airborne it impacts on the atmosphere, and through deposition it provides a nutrient source to oceanic and terrestrial biogeochemical systems. Almost all dust processes are highly size dependent, and a realistic representation of the size distribution is critical for the simulation of the dust atmospheric lifecycle. However, models struggle to represent the evolution of dust size distributions. Processes such as triboelectric charging and non-sphericity have recently to be potentially important processes, yet are not included in dust models. This has knock-on effects on the ability of dust models to accurately represent the impact of dust on human health, infrastructure, weather and climate. Until recently, there has been a lack of observations of large dust particles (>10 microns). However, in the past ten years aircraft observations have utilized new technology to measure the full size range of dust, overcoming limitations of previous measurements. The new observational data include FENNEC near north African sources, AER-D in the west Atlantic and SALTRACE in both east and west Atlantic, providing constraints at various stages of the dust life cycle.The aim of the studentship is to use the new observations to investigate the effect of deposition and transport processes on the dust size distribution, thereby improving our understanding of dust physics and microphysics. The student will do this within the framework of the Met Office Unified Model (UM). Improved understanding of dust transport and deposition will be widely applicable, improving the representation of dust and its impacts in climate models. The studentship is supported by CASE sponsorship from the Met Office and linked to the NCAS-led ACSIS (North Atlantic Climate System Integrated Study) project, since dust transport is important in influencing Atlantic sea surface temperatures. Initially the observational data will be used to evaluate dust in a climate model simulation. Then the contribution of various processes to the evolution of dust size distribution across the Atlantic would be assessed by disabling each existing model process (e.g. sedimentation, convection) in turn, and by introducing novel processes such as the effects of non-sphericity and of triboelectric charging. Key processes would then be selected for more detailed investigation, using either the UM or a box model, with the aim of understanding the causes of size biases and identifying potential improvements. Finally, recommended developments would be tested on a global scale over climate timescales. Improvements will be directly applicable in the Met Office UK Earth System Model and Numerical Weather Prediction models.