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

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.