Further enhancements were made in modeling capabilities of A2C. A2C is a three-dimensional mesoscale/CFD (computational fluid dynamics) combined model. “A2C” stands for “Atmosphere 2 CFD”.

It consists of a wind component A2Cflow and a transport and diffusion component A2Ct&d. A2Ct&d is based on the Lagrangian random puff algorithms and uses as inputs the wind and turbulence distributions predicted by A2Cflow.

The A2C modeling system was used for simulations of air flows and transport and dispersion from wind tunnel to terrain scales. We added a new capability to the A2C modeling system to simulate interactively air flows and transport and diffusion of airborne materials in the exterior and interior of buildings in complex terrain.

The mesoscale part of A2C provided boundary conditions to the CFD part of A2C which was nested in the domain. The CFD part of A2C updated variables in the mesoscale domain. Two-way interaction successfully transferred information to each other.

The outer domain provided diurnal variation of local flows such as sea-land breezes and mountain-valley flows to the inner domain. On the other hand, the inner domain transferred heating and cooling and blocking effects of buildings to the outer domain. Air flows around buildings were greatly modified by heating and cooling of building walls and roofs.

The A2Cflow was based on the Level 2.5 Mellor-Yamada second-moment turbulence -closure equations, where prognostic equations were solved for the turbulence kinetic energy and turbulence length scale. Three dimensional distributions of the turbulence time scale were obtained as the ratios of the length scales to the velocity scales.

Simulations of results will be demonstrated by the computer generated animations.