  We report the experimental observation of novel vortex patterns in a
vertically tapped granular media. Depending on the tapping acceleration two
behaviors are observed. For high acceleration a convection vortex appears in
the whole media whereas for low acceleration two unstable vortices appear in
the upper part of the media and slowly compact the lower part. We explain the
formation of the vortices and relate them to granular convection. Our results
demonstrate the importance of compression waves propagation on granular
compaction.
