The sources, processing and activity of ice nucleating particles in the high latitudes

Lead Research Organisation: University of Leeds
Department Name: School of Earth and Environment

Abstract

Overview
The student will work with leading groups at the Met Office and the University of Leeds to understand the sources and activity of particles which trigger ice formation in high latitude supercooled liquid clouds. Ice formation in these clouds is a major uncertainty impacting the accuracy of climate projections and short term weather forecasts, hence with major societal and commercial implications. Through the use of state-of-the-art and unique instrumentation, from both Leeds and the Met Office, for measuring ice nucleating particles (INPs) in the atmosphere the student will become an expert aerosol scientist with highly marketable knowledge as well as addressing pressing scientific challenges. This will involve work in both the laboratory and during field campaigns using the FAAM BAe-146 research aircraft, and interaction with atmospheric modellers to develop and test INP parametrisations that could be used in the UK Met Office Unified Model.
Background
In the high latitudes, low and mid-level stratiform clouds commonly exist in a supercooled state, where cloud droplets persist well below the melting point of ice. These supercooled clouds are very sensitive to the presence of ice nucleating particles, which are notoriously hard to measure. A supercooled cloud tends to be composed of many small water droplets and can persist for a long period of time and have a high albedo relative to a similar cloud composed of ice. The occurrence of INP leads to the growth of a small number of ice crystals which can grow by vapour diffusion and riming, depleting the supercooled liquid water. These ice particles then sediment, reducing cloud lifetime. Models tend to represent this process extremely poorly (Boeke, 2016), but the new generation of Met Office models are now able to represent the impact of ice nucleation more realistically. Hence, the fundamental understanding of INP concentrations that the student will generate in their PhD will lead to improved weather and climate models which has clear social and economic value.

PhD objectives
The overarching objective is to improve the understanding of the sources, processing and activity of ice nucleating particles in the high latitudes. The scientific objectives will involve:
1. Measuring and characterising the occurrence of INP at high latitudes by taking part in research flights on the FAAM BAe-146 aircraft during aerosol and cloud-physics based field campaigns. Campaigns may include Scotland/Iceland Northeast Atlantic Cold Air Outbreaks and Scandinavia High-latitude cirrus and orographic mid-level clouds.
2. Characterise and validate the Met Office Ice Nucleus Counter (INC) against other INP devices, both in Leeds and at our partner's AIDA facility in Karlsruhe Institute of Technology.
3. Quantify the impact of acid-aging on the ice nucleating ability of desert dust, a critically important INP type, using the Met Office INC and the new Leeds microfluidics INP device. Dust INP in the high latitudes is often transported from the arid source regions in Asia and Africa, but the reactions the dust undergo with time remain un-quantified. The environmental conditions required to trigger ice formation is expected to depend on the aging of the INP.
4. Develop representations of ice nucleation that can be used in numerical models.

Publications

10 25 50