“…Granular convection has been studied extensively at mild fluidization [23,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69], for which the convection is principally boundary-driven. However, the buoyancy-driven convection observed here occurs at high fluidization and this has been reported much more rarely in the literature.…”