CR2025_54 Influence of Surface Roughness on Arctic Cyclones and Their Coupled Interaction with the Climate State in Summer

Lead Supervisor: John Methven, Department of Meteorology, University of Reading

Email: J.Methven@reading.ac.uk

Co-supervisors: Ben Harvey, National Centre for Atmospheric Science and Department of Meteorology, University of Reading; Ambrogio Volonte, Department of Meteorology, University of Reading; Sarah Keely, European Centre for Medium-range Weather Forecasts

Climate change is faster in the Arctic than elsewhere on Earth. As the surface warms the sea ice has become thinner than before over vast areas. Arctic cyclones – the dominant weather systems in the region – are able to make rapid changes in the sea ice distribution through wind stress forcing and moving ice into warmer regions of the ocean where it can melt faster. The winds also generate ocean waves which propagate into the marginal ice zone and result in the break up of ice pack. In addition, changes in surface properties, including sea ice roughness, albedo and surface temperature gradients, are expected to influence the development of Arctic cyclones and their interaction with climate. However, the physical mechanisms behind these coupled interactions are not well understood and their representation in global prediction models are also much more uncertain than in mid-latitudes.

Global weather prediction centres are still gradually increasing the number of coupled components and their interactions represented in their numerical models. The IFS model of ECMWF simulates the atmosphere, ocean, ocean waves and sea ice and some aspects of their interactions (for example, the propagation of waves through the sea ice is soon to be included). However, evaluating and improving these models is challenging, partly because suitable observations for evaluation of coupled processes are very sparse and also because the nature of the mechanisms of coupled interaction are not well understood.

In this project we will focus particularly on the effects of changes in the marginal ice zone on the behaviour of cyclones and the Arctic climate in summer. One hypothesis that we will test is that greater friction over the marginal ice zone (it is rougher when there is partial cover of ice) weakens low level winds in cyclones, and also their heat transports, which indirectly results in a stronger temperature contrast between land and sea ice around the Arctic Ocean coast. Arctic cyclones crossing stronger temperature gradients are expected to grow faster. So a new dynamic climate equilibrium may be attained with stronger gradients and a faster turnover of cyclones.

The project makes use of two opportunities: 1) working with the ECMWF team who are developing the coupled prediction capability in the Arctic, including experimental model versions and a prototype coupled prediction AI model. 2) access to field campaign observations of Arctic cyclones and sea ice gathered by the team in 2022 (Riviere et al., 2024). These will be harnessed to evaluate the representation of coupled processes in the experimental models.

The research will involve several stages. 1) Analysis of global meteorological data and operational IFS coupled predictions (e.g., Croad et al., 2023), focusing on Arctic cyclone characteristics (e.g., number, intensity, longevity) and relation to key aspects of the climate state, such as the temperature gradient across the Arctic Ocean coastal zone, polar jet streams, sea ice fraction and thickness. 2) Designing and running sensitivity experiments (with expert input from the ECMWF team) where surface properties are modified, or model processes changed, and the effects on sea ice and atmospheric near surface fluxes are compared with observations. 3) The hypothesis relating to changes in cyclones and simulated climate state is tested and results interpreted in terms of the existing theories for cyclone dynamics and their interactions with the mean state.

Training opportunities:

On this project you will be based at the University of Reading and interact with the coupled modelling team at ECMWF. You will have the opportunity to work at ECMWF with the team, particularly for setting up experiments on their computing system. You will be able to run your experiments using the centre’s supercomputing facilities. The ECWMF is a world leading global prediction centre with headquarters in Reading. You will also be able to take MSc modules unique to Reading, such as Advanced Atmospheric Dynamics, and week-long training workshops at ECMWF, for example on Atmospheric Parametrization. 

Student profile:

This project is suitable for a student with a degree in physics, mathematics or other mathematically intensive science subject. Skills in computer programming are expected. Experience using numerical models is highly desirable but not a requirement. 

Co-Sponsorship details:

The project includes a placement opportunity at the European Centre for Medium-range Weather Forecasts.

References:

• Croad, H. L., Methven, J., Harvey, B. J., Keeley, S. P. E., and Volonte, A. (2023). The role of boundary layer processes in summer-time Arctic cyclones. Weather Clim. Dyn., 4, 617-638, doi.org/10.5194/wcd-4-617-2023.
• Riviere, G. et al. (2024). The THINICE field campaign: Interactions between Arctic cyclones, tropopause polar vortices, clouds and sea ice in summer. Bull. Am. Meteorol. Soc. , Early View, doi.org/10.1175/BAMS-D-23-0143.1.