Viability of the Yin-Yang Grid as a Basis for Future Generations of Atmospheric Models
Goddard, Jacqueline Clare
Thesis or dissertation
University of Exeter
This thesis concerns the viability of the `Yin-Yang grid' for future generations of atmospheric models. The `Yin-Yang grid’, is an overset grid in which two segments of the classical latitude-longitude grid, with the poles excised, are rotated relative to each other and fit together rather like the surface of a tennis ball. We investigate whether wave propagation can be accurately modelled across the overlap regions and whether transport of air mass properties, such as entropy or water content, can be modelled accurately and conservatively across the overlap regions, without significant `grid imprinting' on the solution. The wave propagation results demonstrate that the overlapping regions support computational/spurious wave modes and methods for controlling these wave modes are discussed. Transport schemes are investigated in one dimension using the Chesshire and Henshaw conservative interpolation scheme [Chesshire and Henshaw 1984] and the new `Zerroukat mass fixer' scheme. The Zerroukat mass fixer scheme is extended to the (two-dimensional) Yin-Yang grid. The results demonstrate that the Zerroukat mass fixer scheme is successful in conserving mass. However, the Zerroukat scheme has an effect on flux limiter schemes, overshoots can occur. The Zerroukat scheme also reduces convergence rates by 2 orders of accuracy. Therefore if 2nd order convergence is required a 4th order scheme would need to be used.
PhD in Mathematics