From gas to ice giants: A unified mechanism for equatorial jets

Abstract

The equatorial jets dominating the dynamics of the Jovian planets exhibit two distinct types of zonal flows: strongly eastward in the gas giants (superrotation) and strongly westward in the ice giants (subrotation). Existing theories propose different mechanisms for these patterns, but no single mechanism has successfully explained both. However, the planetary parameters of the four Solar System giant planets suggest that a fundamentally different mechanism is unlikely. In this study, we show that convection-driven columnar structures can account for both eastward and westward equatorial jets, framing the phenomenon as a bifurcation. Consequently, both superrotation and subrotation emerge as stable branches of the same mechanistic solution. Our analysis of these solutions uncovers similarities in the properties of equatorial waves and the leading-order momentum balance. This study suggests that the fundamental dynamics governing equatorial jet formation may be more broadly applicable across the Jovian planets than previously believed, offering a unified explanation for their two distinct zonal wind patterns.