It is well known that light gases tend to diffuse upward (see this PSE question and answer). Helium is even slowly escaping the Earth, because many molecules have velocities higher than the escape one, near the space boundary.
On the other hand, it is also well known that bigger cereals tend to be on the top of a (shaken) cereal bag. This effect is called granular convection, but seems to go in counter with the lighter object moving higher.
Thus, I guess that gas molecules (or atoms) are subject to several forces and effects, even granular convection. My question is, to which extent is granular convection acting on gas molecules composing the atmosphere?
