Background
Global models underpinning future projections struggle to capture African weather and climate change, to a large extent because the convective storms that generate tropical rainfall are below their coarse grid scale and have to be parameterised. Convection-permitting (CP) simulations using km-scale grids significantly reduce errors, but presently only cover short realisations of a single climate scenario. Quantifying risk requires a multi-model ensemble that covers a range of scenarios and accurately captures the atmospheric processes key to representing how weather evolves under climate change. Project partner the Met Office are thus running the first ever tropical CP ensemble, CP4A, driven by a range of global models. The open challenge is to understand how we can combine information from such models with global simulations, observations and theory to give accurate ranges of uncertainty on future projections of user-relevant quantities, such as extreme rain or monsoon onset.
PhD opportunity
This project will explore how physical understanding from high-resolution ensembles run for a decade or less can be combined with coarser-grid global or regional climate projections, run for many decades, to improve estimates of climate uncertainty. We will focus on West Africa, where deep convective storms dominate the regional climate and are often coupled to African Easterly Waves (AEWs), synoptic-scale features which influence Atlantic hurricane development. Rainfall intensity for such storms scales with environmental factors, such as wind-shear and moisture, themselves modulated by AEWs and other tropical wave modes. We will evaluate these mechanisms in CP4A, and quantify the spread in future environmental conditions and changes in wave properties (eg periodicity, magnitude, latitude). Together, this will enable a comprehensive process-based understanding of projected changes to rainfall and wave activity in the high-resolution ensemble, and of the couplings between them.
Building from our insights from the CP4A ensemble, we will interrogate the responsible mechanisms in global models, and synthesise the understanding derived from these complementary data sources to provide improved estimates of risks and uncertainties. This will enable updates, and we anticipate improvements, to user-relevant information, whose metrics (eg rainfall extremes, monsoon onset) can be chosen based on the project’s development. There is also scope to apply analysis from the high-resolution ensemble to explore and test methods such as machine learning climate downscaling techniques. The project offers an opportunity to combine fundamental atmospheric dynamics with a robust analysis of future climate uncertainty, building expertise at the intersection of climate and weather science. The results will directly feed into model evaluation processes at the Met Office, and contribute to improving tropical climate projections.
Other information
This project would suit a student interested in exploring the physics of Earth’s present and future atmosphere, and using their science to deliver tangible impact. A strong background in atmospheric science, fluid dynamics or similar mathematics/physics is therefore desirable. While the project will be tailored to the student’s interests, it will combine both process-based analysis and robust uncertainty quantification. The student will not be expected to run new simulations of their own, but there is scope to facilitate this if of interest. Travel to Africa is not required, but there may be opportunities for this resulting from other projects.
The project would be within the Atmospheric and Cloud Dynamics group of ICAS, https://environment.leeds.ac.uk/atmospheric-cloud-dynamics.
- Existing trends in West African deep convection: Taylor et al, “Frequency of extreme Sahelian storms tripled since 1982 in satellite observations”, Nature, 2017. http://dx.doi.org/10.1038/nature22069
- Environmental controls on convective storms in modern Met Office models: Maybee et al, “Wind shear in convection-permitting models influence MCS rainfall and forcing of tropical circulation”, Geophysical Research Letters, 2024. https://doi.org/10.1029/2024GL110119
- Results from older, single climate-scenario CP4A simulations: Senior et al, “Convection permitting regional climate change simulations for understanding future climate and informing decision making in Africa”, Bulletin of the American Meteorological Society, 2021.https://doi.org/10.1175/BAMS-D-20-0020.1
- Using high-resolution models to improve climate projections: Klein et al, “Combining CMIP data with a regional convection-permitting model and observations to project extreme rainfall under climate change”, Environmental Research Letters, 2021. https://doi.org/10.1088/1748-9326/ac26f1
- Effect of environmental moisture in influencing AEW propagation and tropical cyclone development: Núñez Ocasio et al, “Moisture Dependence of an African Easterly Wave Within the West African Monsoon System”, Journal of Advances in Modelling Atmospheric Systems, 2024. https://doi.org/10.1029/2023MS004070