An efficient highly parallel multigrid method for the advection operator **This research was supported by the National Aeronautics and Space Administration under NASA Contract No. NAS1-97046 while the authors were in residence at the Institute for Computer Applications in Science and Engineering (ICASE), NASA Langley Research Center, Hampton, VA 23681-2199. Ignacio M. Llorente and Ruben S. Montero were also supported in part by the Spanish research grant TIC 99/0474 | Publicación