The Mixing Layer Terrain Wind Adjustment Model (MILTWAM) for Airflow over Complex Terrain

This paper presents the Mixing Layer Terrain Wind Adjustment Model (MILTWAM) for airflow over complex terrain. MILTWAM is a diagnostic, mass-consistent, wind-field model based on NUATMOS (Ross, 1988). It is specifically designed for use in the D2-Puff dispersion model developed by Innovative Emergency Management Inc. and it produces realistic estimates of winds, even when only a few wind observations are available. This model is also fast enough for use in an emergency response dispersion model that runs on a personal computer (PC). Key features of the MILTWAM model are:

1. The height of the top of the mixing layer is explicitly included in the model and imposes a non-porous upper lid on the flow. This upper lid is a major influence in determining the flow over the terrain.

2. A three-dimensional model with terrain-following coordinates is used when the top of the mixing layer is above the highest terrain; a vertically-averaged two-dimensional model is used when the mixing layer is below the highest terrain.

3. The winds output by the model are designed to agree with the observed winds at the observation points.

Model results are shown for simple geometric terrain and for real terrain.