<title>Simulation of aerosol cloud transport and diffusion with OMEGA</title>

Abstract

The Operational Multiscale Environment model with Grid Adaptivity (OMEGA) is a new atmospheric simulation system that merges state-of-the-art computational fluid dynamics techniques with a comprehensive non-hydrostatic equation set. OMEGA is based upon an unstructured triangular prism grid that permits a horizontal grid resolution ranging from 100 km down to 1 km and a vertical resolution from a few tens of meters in the boundary layer to 1 km in the free troposphere. OMEGA also contains an embedded aerosol transport algorithm that permits the simulation at high resolution of the transport and diffusion of either grid-based aerosols or of Lagrangian parcels. OMEGA represents a significant advance in the field of weather prediction and aerosol transport. Current operational forecast models are scale- specific and have a limit to their resolution caused by their fixed rectangular grid structure. OMEGA, on the other hand, is naturally scale spanning and its unstructured grid permits the addition of grid elements at any point in space and time. This means that OMEGA can readily adapt its grid to fixed surface or terrain features, or dynamic features in the evolving weather. In addition, OMEGA can provide enhanced grid resolution in localized regions such as in the vicinity of a dust, smoke, or chemical cloud. The flexible grid adaptivity of OMEGA provides it with an important advantage over previous models. It permits the resolution of orographic and land/water boundary features improving the fine scale meteorological simulation and, in turn, the simulation of the aerosol transport. The coupling of a very high resolution (1 km) atmospheric simulation tool with an aerosol transport and diffusion model creates a flexible tool for a variety of applications and scales to be used anywhere that small scale features could have an impact on the local meteorology. Among these is aerosol transport in complex terrain and near land/water boundaries. In this paper, we will present an overview of the atmospheric simulation capabilities of OMEGA. We will discuss both its numerical techniques and its physics. We will also present an overview of the aerosol transport and diffusion model included in OMEGA; both its physical basis as well as its implementation on the adaptive unstructured grid that forms the basis of OMEGA. We will then discuss the application of this aerosol transport capability to the problem of simulating the transport of dust, smoke, or chemical clouds.