P2M.9 Effects of explicit numerical diffusion in simulations of mesoscale circulations by the Advanced Research WRF Model

Tuesday, 25 October 2005
Alvarado F and Atria (Hotel Albuquerque at Old Town)
Jason C. Knievel, NCAR, Boulder, CO; and G. H. Bryan and J. P. Hacker

The high effective resolution of the WRF Model (Advanced Research core) is partly due to the implicit, scale-selective diffusion characteristic of the model's high-order advection scheme. This implicit diffusion is proportional to the speed of the advecting wind, so in light wind the diffusion is weak. In some cases the diffusion is too weak to filter small, poorly resolved kinematical features that can grow until the overwhelm mesoscale circulations in the boundary layer, such as lake breezes and slope winds.

To mitigate this problem, the authors added to the WRF Model an explicit numerical diffusion scheme. The scheme is 6th-order, so its scale-selectivity preserves the WRF Model's high effective resolution. The scheme is also monotonic because it does not permit diffusion up gradients in physical fields. The authors will explain the diffusion scheme and will demonstrate how it improves forecasts of mesoscale circulations in the boundary layer.

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