Granular particles subject to both vertical gas flow and vertical vibration are shown experimentally to exhibit structured convection cells in a densely packed yet fluidized state without gas voids traveling through the particles. Continuum gas-granular simulations reproduce the phenomenon and demonstrate that the convection occurs due to buoyant force arising from a positive vertical gradient in bulk solid density competing with viscous force created by interparticle friction. Simulations further show that convection structures persist in a controllable manner when increasing system width.