Further enhancements were made in modeling capabilities of A2C where “A2C” stands for “Atmosphere to CFD”. A2C is a three-dimensional mesoscale and CFD scale forecast modeling system. The modeling system consists of a wind component A2Cflow and a transport and diffusion component A2Ct&d where “t&d “stands for “transport and diffusion”. A2Cflow is based on the Mellor-Yamada second-moment turbulence-closure equations. A2Ct&d is based on the Lagrangian random puff algorithms and uses as inputs the wind and turbulence distributions predicted by A2Cflow.

A2Cflow simulated successfully separation, recirculation, and reattachment of air flows around obstacles placed in a wind tunnel where a horizontal grid spacing of 2 cm was used in simulations. The same model was used to simulate air flows around a cluster of buildings under the influence of diurnal variations of mesoscale weather conditions such as sea- and land-breezes. A nesting method was applied to capture a large scale terrain and a small scale building variations. Horizontal grid spacing of 10 m for the inner domain and 40 m to 160 m for the outer domains were used.

Temperatures of building walls and roofs were computed by solving a one-dimensional heat conduction equation in the direction perpendicular to the walls and roofs. The boundary conditions were heat balance equations at the outer sides of walls and roofs while temperatures at the inner sides of the walls were assumed to be the same as the room temperatures.

Recently 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. Tracers were released at the upwind side of an opening of a building and concentration distributions in the exterior and interior of buildings were simulated.

High concentration values were computed in the interior of a building where closed circulations were predicted and wind speeds were relatively small. The new capabilities are useful for emergency response planning to investigate the consequence of toxic materials released in the exterior or interior of a building in complex terrain.

The A2C modeling system was used to simulate air flows from building to terrain scales. It was applied to simulate air flows and transport of airborne materials over complex terrain, around buildings, and indoors. Buildings were placed in complex terrain and building wall and roof temperatures were also computed. The modeling system runs on the Windows environment and is equipped with extensive graphics capabilities including 2d and 3d animations. We will demonstrate the modeling capabilities through animations of simulation results.