Hydrodynamics of thermal granular convection.

A hydrodynamic theory is formulated for buoyancy-driven (``thermal'') granular convection, recently predicted in molecular dynamic simulations and observed in experiment. The limit of a dilute flow is considered. The problem is fully described by three scaled parameters. The convection occurs via a supercritical bifurcation, the inelasticity of the collisions being the control parameter. The character of hydrodynamic modes of the system is discussed. The theory is expected to be valid for small Knudsen numbers and nearly elastic grain collisions.