  Super-rotations of the planetary atmosphere are reconsidered from the
dynamical point of view. In particular, we emphasize that the super-rotation
appears spontaneously without any explicit force. Although the super-rotation
violates the bilateral symmetry (east-west reflection symmetry) of the system,
this violation is spontaneous. Constructing a minimal model that derives the
super-rotation, we clarify the condition for the super-rotation to appear. We
find that the flow is always determined autonomously so that the flow speed
becomes maximum or the temperature difference smallest. After constraining the
parameters of the model from observations, we compare our model with the others
most of which demand the explicit symmetry violation due to the planetary
rotation.
