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Understanding microscale atmospheric flows using numerical models requires resolving dynamics over steep and complex terrain. The use of terrain-following coordinates in many atmospheric models arguably limits the stability of the model solutions where steep orography is introduced, and can result in diffusion in anisotropic cells.

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Terrain-following (left panel) and terrain-intersecting co-ordinate systems.

Steppeler et al. (Monthly Weather Review, 134, pp3625-3643, 2006) suggest terrain-following grids under-predict precipitation over steep orography. A new high-resolution model which will enable the resolution of flow over steep terrain and other atmospheric high resolution processes in the atmosphere is being developed at the University of Leeds. This three-dimensional model uses terrain-intersecting co-ordinates, incorporating an established lower boundary scheme (LMz), and solves the full equation set on a Charney-Phillips grid.

microscalea

Comparison between the new (VHREM) model (upper panel) and BLASIUS for a simple heat bubble experiment. With thanks to Sarah Jane Lock (University of Leeds) for the VHREM results.

Further information see the Microscale Modelling Homepage

Staff involved in this activity are

Dr Alan Gadian (University of Leeds)