Even in "still" air, the individual molecules have random velocities due to temperature - on the order of 100 m/s. Combined with the fact that there are more mi

Even in "still" air, the individual molecules have random velocities due to temperature - on the order of 100 m/s. Combined with the fact that there are more mixed configurations than unmixed configurations (entropy of mixing), this randomness effectively stirs the atmosphere without the need for the bulk motion of the wind.