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Tuesday 29 Nov 2022Unconventional ways of modelling the atmosphere: convection, advection and adaptivity

Hilary Weller - University of Reading

Harrison 170 14:30-15:30

This talk will describe three unconventional ways of modelling the atmosphere:

  1. Multi-fluid modelling of buoyant convection

  2. Implicit time stepping to take long time steps for advection

  3. Moving meshes over mountains for adaptivity.

Multi-fluid modelling has been introduced in order to overcome some of the limitations of mass-flux convection schemes. Mass flux schemes assume an equilibrium and they assume that the compensating descent from convection is local. Multi-fluid modelling is introduced to overcome these deficiencies.
Implicit time stepping for advection is not popular in atmospheric science because of the cost of the global matrix solution and the phase errors for large Courant numbers. However, implicit advection is simple to implement, conservative on any grid structure and can exploit improvements in solver efficiency and parallelisation. I will describe an implicit version of the MPDATA advection scheme and show that it is accurate for low Courant numbers, stable for very large Courant numbers and locally high Courant numbers (such as occur over the poles of a latitude-longitude grid) do not harm the accuracy.
Finally I will talk about adaptivity using moving meshes. When meshes adapt over mountains, the total volume of the fluid domain can change, making conservation impossible. I will introduce a fix that does not require calculating and keeping track of moving volumes but leads to exact conservation of volume and preservation of uniform fields.

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