This project forms part of my Open Fellowship grant, which you can read more about here.
Background
The growth of cloud droplets into raindrops is controlled by countless collisions between micron-sized drops. Whether two drops merge, bounce apart, or fragment into smaller droplets depends on complex interfacial physics, including nanoscale gas films and the turbulent environment in which collisions occur (see our work in this area).
Current weather and climate models use “collision maps” — simple look-up tables that assign an outcome to each collision. But most of these maps date from laboratory experiments and numerical studies in the 1980s. They assume, for example, that any drops which touch will coalesce, which we now know to be wrong. This is likely to lead to systematic errors in cloud dynamics, with major implications for forecasting and climate modelling.
Objectives
- Develop modern collision maps that capture the full range of possible outcomes: bouncing, merging, and fragmentation.
- Quantify how nanoscale processes (gas nanofilms, fluctuation-driven instabilities) influence outcomes under realistic cloud conditions.
- Provide parameterisations (collision kernels) suitable for direct use in cloud-resolving and weather/climate models.
Approach
This project will combine high-fidelity simulation and physical modelling:
- Develop mathematical models for nanofilm dynamics in three-dimensions that captures flow-governing small-scale physics.
- Create an open-source computational capability for simulating drop collisions.
- Work closely with collaborators (e.g. in atmospheric science) to ensure compatibility with their operational models.
Collaborators
- Met Office (UK) – implementation in the Unified Model and direct impact on UK forecasting.
- NCAR (USA) – development of Lagrangian super-droplet methods for climate models.
- Syngenta (UK) – informing models for agricultural spraying technologies.
- Experimental groups in Twente (Lohse) and EPFL (Kolinski) – cutting-edge laboratory experiments to validate simulations.
What’s involved
The researcher will gain expertise in state-of-the-art modelling of droplet collisions and in advanced numerical methods for simulating multiphase flows. They will also develop skills in connecting these fundamental simulations to atmospheric and climate models, ensuring real-world impact. The project is highly collaborative: the researcher will work with leading international partners, with opportunities to visit experimental laboratories and atmospheric science centres abroad. In addition, the role comes with strong support for personal development, including funded opportunities to organise workshops, build networks, and shape the emerging research community.
James Sprittles 