With the release of version 2.2, the Advanced Research core of the Weather Research and Forecasting (WRF) Model includes, for the first time, an explicit, sixth-order, numerical diffusion scheme. This scheme's scale-selectivity preserves the model's high effective resolution. The scheme also can be made monotonic, so extrema are not created nor amplified in the field being diffused. Making the scheme monotonic, however, compromises the diffusion's rate and scale-selectivity.

Recent research has shown that the explicit diffusion scheme can dramatically suppress noise within the daytime boundary layer. Because one manifestation of the noise is deep, alternating columns of ascent and descent, whether and how the noise is suppressed may affect the transport and dispersion of airborne material released into the boundary layer.

The presenters will cover the main features of the new explicit diffusion scheme and will use idealized tests to explore the details of how forced monotonicity alters the scheme's diffusion rate and scale selectivity. The presenters then will show how explicit diffusion in the WRF Model affects the vertical and horizontal transport and dispersion of airborne material in the boundary layer.