Aircraft measurements of ice-nucleating particles and their importance for mixed-phase clouds

Overview

You 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 clouds. Ice formation in clouds is poorly understood leading to major uncertainties in projections of climate and extreme weather events. You will take part in the Wessex Summer Convection Experiment (WesCon) aircraft campaign focused on summertime convective clouds in Southern England. Through the use of state-of-the-art and unique instrumentation for measuring ice nucleating particles (INPs) in the atmosphere you will become an expert aerosol scientist with highly marketable knowledge as well as addressing pressing scientific challenges. One of our hypotheses is that biological INPs as well as desert dust aerosol are extremely important in determining the properties of these clouds.  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.  The project is a Met Office CASE supported and you will work closely with supervisors both in Leeds and the Met Office.

Objectives

The overarching objective is to improve the understanding of the sources, processing and activity of ice nucleating particles relevant for mixed-phase clouds. The scientific objectives will involve:

  1. Work with the Met Office to characterise and validate their new Ice Nucleus Counter (INC) against other INP devices, both in Leeds and at our partner’s AIDA facility in Karlsruhe Institute of Technology.
  2. Work in Leeds to develop the complementary filter based INP analysis and increase its sensitivity in order to quantify INP at temperatures relevant for the initiation of secondary ice production and distinguish between biological and mineral ice nucleating materials.
  3. Measure and characterise the occurrence of INP in the WesCon field campaign which has a focus on convective clouds in southern England. This will involve taking part in research flights on the FAAM BAe-146 aircraft in summer 2023.
  4. Measure and characterise INP relevant for cold-air outbreaks as part of our ongoing programme of research in this area.
  5. Work with the modellers in WesCon to define primary ice production using the results from the campaign.

Case partner

In this project you will work closely with Dr Richard Cotton and Dr Steven Abel who are both Met Office scientists.  Richard has developed an aircraft instrument for measuring INPs and you will help him validate and deploy this instrument.  Both Steven and Richard are heavily involved in FAAM field campaigns around the world and you will work directly with them in the field.  The CASE aware provides an enhanced research support grant and there are additional Met Office funds to pay for involvement in the field campaigns, so funds will not likely be a limit to your ambitions.

Research environment

You will join the vibrant Ice Nucleation group in the Institute for Climate and Atmospheric Science (ICAS). ICAS covers climate, air pollution, meteorology and climate impacts, with extensive programmes in observations, modelling and lab studies. Atmospheric science at Leeds is ranked 9th in the Centre for World University Rankings (http://cwur.org/2017) and 13th in the Academic Ranking of World Universities out of 400 (http://www.shanghairanking.com). Wider interdisciplinary experience is guaranteed through our new cross-campus Priestley Centre (http://climate.leeds.ac.uk). Peer exchange and learning occurs through frequent institute and group seminars, discussion meetings and paper review groups.

We also have formal partnerships with both the UK Met Office and also the Karlsruhe Institute of Technology. The KIT-ICAS partnership has led to exchange of students and staff and many joint publications.

The supervisors have an outstanding track record of PhD student supervision, with students having won the Aerosol Society’s Doctoral Thesis prize, the School of Earth and Environment PhD publication prize (out of 200 students), the Piers Sellers Priestly prize as well as several national and international prizes.

Background science

Atmospheric ice-nucleating particles (INP) are aerosol particles with special physical and chemical properties that enable them to induce the formation of ice crystals in clouds below 0°C. In the absence of INP, cloud droplets can supercool to below -33°C. Formation of ice in clouds is a fundamental process that initiates most of the global precipitation and can lead to invigoration of convective storms. It also has profound effects on the radiative properties of clouds and thereby influences the effect that clouds have on climate. For example, we recently demonstrated that the low INP concentrations above the Southern Ocean leads to clouds which persist in a supercooled state, but are extremely sensitive to changes in INP concentration (Vergara-Temprado, 2018).

There are different types of clouds in which ice is important, but the type and mode of action through which INP nucleate ice is distinct in the different cloud regimes. In the lower and mid troposphere at temperatures between 0 and -35oC clouds can exist as supercooled water, ice or a mixture of the two. In this regime, INP tend to be immersed in supercooled water before they can trigger freezing.  In contrast, in the upper troposphere under cirrus conditions ice can form directly onto aerosol particles well below the supersaturation required to form a liquid cloud.  In fact, different populations of aerosol serve as INPs in the different cloud regimes, hence measurements need to be made that distinguish between these different populations.

Our understanding of INP sources in the atmosphere, and hence their impact on climate, is in its infancy. Substantial developments are being made by characterizing INP in innovative laboratory and field experiments, and then carrying this new knowledge into atmospheric models. For example, the Leeds group discovered that a specific mineral group in desert dust particles can explain their ice nucleating properties, enabling a global model of these INP to be developed (Atkinson et al., 2013). Similarly, we quantified marine organic INP through field measurements in remote environments from research ships and then used our global model to represent the global distribution of these INP (Wilson et al. 2015).

Requirements

Undergraduate training in any physical/chemical/meteorological/biological science or engineering would be appropriate. We are a multi-disciplinary group and greatly benefit from team members with diverse backgrounds. The project can be tuned to fit an ambitious student’s interests and skills.

Training

Students will receive highly transferrable training in aerosol science and technology as well specialist training in the field of atmospheric ice nucleation.  Co-supervision will involve regular online meetings with all supervisors. In addition the successful PhD student will have access to a broad spectrum of training workshops put on by the Faculty that include an extensive range of supportive workshops in skills such as managing your degree to preparing for your viva.  There will also be opportunities to take part in field campaigns, international conferences, and training courses offered by other organisations such as the Aerosol Society.

Reading

Here are a few papers that provide a nice background to the project:

A study where we characterised the ice nucleating ability of dust from Iceland using the FAAM aircraft: Sanchez-Marroquin et al., Iceland is an episodic source of atmospheric ice-nucleating particles relevant for mixed-phase clouds, Science Advances, 2020

We’ve found that INP over Southern England are often biological in nature: Sanchez-Marroquin et al., Mineral and biological ice-nucleating particles above the South East of the British Isles, Env Sci: Atm, 2021.

We set out why ice nucleating particles are very important for climate here: Murray et al., Cloud-phase climate feedback and the importance of ice-nucleating particles, ACP,  2021

We’ve also show that INP spectra a very important for defining the properties of deep convective clouds (this one is a bit more detailed, but take a look at the abstract): Hawker et al.  The temperature dependence of ice-nucleating particle concentrations affects the radiative properties of tropical convective cloud systems,  ACP 2021.