Editorial Type:
Article
Article Type:
Research Article

Explicit Numerical Diffusion in the WRF Model

Jason C. Knievel National Center for Atmospheric Research,* Boulder, Colorado

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George H. Bryan National Center for Atmospheric Research,* Boulder, Colorado

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Joshua P. Hacker National Center for Atmospheric Research,* Boulder, Colorado

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Print Publication:
01 Nov 2007
DOI:
https://doi.org/10.1175/2007MWR2100.1
Page(s):
3808–3824
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Abstract

Diffusion that is implicit in the odd-ordered advection schemes in early versions of the Advanced Research core of the Weather Research and Forecasting (WRF) model is sometimes insufficient to remove noise from kinematical fields. The problem is worst when grid-relative wind speeds are low and when stratification is nearly neutral or unstable, such as in weakly forced daytime boundary layers, where noise can grow until it competes with the physical phenomena being simulated. One solution to this problem is an explicit, sixth-order numerical diffusion scheme that preserves the WRF model’s high effective resolution and uses a flux limiter to ensure monotonicity. The scheme, and how it was added to the WRF model, are explained. The scheme is then demonstrated in an idealized framework and in simulations of salt breezes and lake breezes in northwestern Utah.

Corresponding author address: Dr. Jason Knievel, NCAR, 3450 Mitchell Ln., Boulder, CO 80301. Email: knievel@ucar.edu

Abstract

Diffusion that is implicit in the odd-ordered advection schemes in early versions of the Advanced Research core of the Weather Research and Forecasting (WRF) model is sometimes insufficient to remove noise from kinematical fields. The problem is worst when grid-relative wind speeds are low and when stratification is nearly neutral or unstable, such as in weakly forced daytime boundary layers, where noise can grow until it competes with the physical phenomena being simulated. One solution to this problem is an explicit, sixth-order numerical diffusion scheme that preserves the WRF model’s high effective resolution and uses a flux limiter to ensure monotonicity. The scheme, and how it was added to the WRF model, are explained. The scheme is then demonstrated in an idealized framework and in simulations of salt breezes and lake breezes in northwestern Utah.

Corresponding author address: Dr. Jason Knievel, NCAR, 3450 Mitchell Ln., Boulder, CO 80301. Email: knievel@ucar.edu

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