Spontaneous Super-Rotation on Planets

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.