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Mr Daniel Joe Griffin

Postgraduate

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After obtaining my MMath degree from the University of Exeter, I joined as a postgraduate researcher in September 2014. I am working in the Centre for Geophysical and Astrophysical Fluid Dynamics with Professor John Thuburn. My postgraduate research is on the extension of the Met Office's Unified Model for weather and climate dynamical core ENDGame (Even Newer Dynamics for General Atmospheric Modelling of the Environment) into the thermosphere.

Currently, ENDGame is able to simulate the atmosphere and remain stable with a top boundary of ~100km. However, the simulation does not currently remain stable if the top boundary is lifted higher than this. This is due to numerical methods generating an excessive imbalance in the troposphere and distorting the vertical propagation of waves into the thermosphere [Griffin and Thuburn, 2017]. However, it is also found that including the physical process of molecular viscosity and diffusion may prevent the excessive growth of waves into the thermosphere, which could improve ENDGame's stability as it is extended into a whole-atmosphere model. The ultimate aim is to develop ENDGame into a whole-atmosphere model that can simulate the Earth's atmosphere from the surface to the exobase at ~600km. A whole-atmosphere version of ENDGame will eventually have useful applications for the Met Office in space weather forecasting.

The short timescale of molecular viscosity and diffusion in the thermosphere demanded an implicit treatment, coupled with the semi-implicit treatment of the dynamics. Treating the molecular viscosity and diffusion in this way was a non-trivial mathematical problem which required the development of a novel numerical solver to solve the coupled system efficiently. It turns out that in a 1D column version of ENDGame, realistic molecular viscosity and diffusion and a modest amount of artificial damping are sufficient to control wave amplitudes and to stabilise the model up to altitudes of 600km. Results in 3D are currently being produced and are forthcoming.

My position as a postgraduate researcher has enabled me to present my research at the European Meteorological Society conference in Dublin, as well as giving seminars at the universities of Exeter and Bath and at the Met Office. I have partaken in poster presentations to explain my work to individuals, catering to their varying levels of familiarity with the field. I have also had the opportunity to publish my research on numerical wave propagation, and am in the process of preparing for publication the results of the developments I have made to the Met Office weather and climate model. I was also able to communicate my work successfully to the Natural Environment Research Council (NERC) in order to secure a grant to work at the Met Office for 6 months. As a result of this placement, I have been able to collaborate and discuss my work with Met Office scientists to work towards implementing my model improvements in an operational capacity.

D. J. Griffin, J. Thuburn. 2018. Numerical Effects on Vertical Wave Propagation in Deep Atmosphere Models, Quarterly Journal of the Royal Meteorological Society.

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