From Gas to Ice Giants: A Unified Mechanism for Equatorial Jets

The equatorial jets observed on the Jovian planets—Jupiter, Saturn, Uranus, and Neptune—exhibit extreme zonal flow patterns, manifesting as either strongly prograde (in the gas giants) or strongly retrograde (in the ice giants). Existing theories have often treated gas giants and ice giants separately, primarily focusing on the differences between deep and shallow dynamics. However, gravity measurements from the Juno spacecraft have revealed that Jupiter's convective envelope may share similarities with those of the ice giants, challenging traditional distinctions between these planetary types and highlighting the potential for a unified explanation.

We present results from a convection-driven anelastic General Circulation Model that introduces a unifying mechanism to explain the equatorial jets on all four Jovian planets. In these simulations, the convective dynamics and planetary rotation drive the formation of tilted convection columns that extend cylindrically from the deep interior to the outer atmospheric layers. These columns play a crucial role in shaping zonal wind patterns, with the tilting of the convection columns introducing asymmetries in momentum transport that lead to the bifurcation of the flow into either superrotation (prograde jets) or subrotation (retrograde jets) in the equatorial region.

Through a detailed analysis of the convection-driven columnar structures, we demonstrate that the equatorial wave properties and the leading-order momentum balance share remarkable similarities across different planetary types. Our findings comprehensively explain the potential for both equatorial superrotation and subrotation under constant physical conditions, thereby elucidating the diverse zonal wind patterns observed on the Jovian planets and providing deeper insight into the mechanisms driving equatorial jet formation. Furthermore, the Juno Microwave Radiometer (MWR) may provide evidence for such tilted convection structures, underscoring the necessity of a thorough understanding of their dynamical contributions.