MUSICA Version 0 represents a regionally refined version of the CAM-chem global chemistry climate model. This model development takes advantage of the Spectral Element (SE) dynamical core (which is an unstructured grid mesh based on a cubed sphere) which now allows for regional refinement (RR). Initial MUSICA-V0 simulations use a grid mesh with global horizontal resolution of 1˚ that refines to 0.125˚ (~14km) over the conterminous U.S. (CONUS).