  We experimentally study the velocity scaling of granular convection which is
a possible mechanism of the regolith migration on the surface of small
asteroids. In order to evaluate the contribution of granular convection to the
regolith migration, the velocity of granular convection under the microgravity
condition has to be revealed. Although it is hard to control the gravitational
acceleration in laboratory experiments, scaling relations involving the
gravitational effect can be evaluated by systematic experiments. Therefore, we
perform such a systematic experiment of the vibration-induced granular
convection. From the experimental data, a scaling form for the granular
convective velocity is obtained. The obtained scaling form implies that the
granular convective velocity can be decomposed into two characteristic velocity
components: vibrational and gravitational velocities. In addition, the system
size dependence is also scaled. According to the scaling form, the granular
convective velocity $v$ depends on the gravitational acceleration $g$ as $v
\propto g^{0.97}$ when the normalized vibrational acceleration is fixed.
