 The MesoNH atmospheric simulation system is a joint effort between the Sinter-National de Richerche's meteorologics and laboratoire derology. It is designed as a research tool for small and mesoscale atmospheric processes, with features such as a numerical model that simulates atmospheric motions ranging from large to micro-scales, a flexible file manager, and an ensemble of interactive procedures to control these functions. The system uses Fortran 90 compiler and is tailored to be easily implemented on any Unix machine. It allows for the transport and diffusion of passive scalars, coupled with a chemical module, and is freely accessible to the research community. This article was authored by J.P. Lafour, J. Stein, and Asensio, and others. We are article.tv. Links in the description below.