Research objectives and content
An accurate representation of tracer transport and mixing by the atmospheric flow is essential to model and predict chemical distributions in the atmosphere. This representation requires a complete understanding of what controls the transport patterns, characterised by their inhomogeneity and the presence of leaky barriers, and of how the formation of microstructure leads to mixing. The predictions of two-dimensional chaotic advection models appear relevant, but neglect of horizontal divergence, vertical advection and vertical microstructure is, however, a serious drawback. This project will extend such simple models to include these three-dimensional effects and compare the predictions with results from numerical simulations and with observations.
One focus will be on how transport barriers are affected by
vertical advection and horizontal divergence. Diagnostics of three-dimensional transport will be developed and validated on idealised models, and then applied to calculations based on observed winds.
A second focus will be on the implications of vertical
microstructure for mixing and diffusion. The concept of an effective horizontal diffusivity accounting for the formation of vertical gradients will be validated. Using theoretical results on microstructure, a systematic technique to infer the value of the diffusivity from airborne data will be devised and applied to large datasets.
Training content (objective, benefit and expected impact)
The project combines theoretical work, numerical modelling and data analysis. The applicant will thus considerably broaden his area of expertise in atmospheric dynamics, notably in state-of-the-art numerical simulations and in modern data analysis techniques. These two domains are in rapid development and now constitute key elements in atmospheric research. The close connection of the project with atmospheric chemical modelling will also lead to important training benefits in this area. More generally, the variety of research currently carried out in DAMTP and particularly in the Atmospheric Dynamics group will offer many training opportunities.