Energetic Control of Atmospheric Regime Transitions

Atmospheric superrotation is commonly associated with the formation of strong eastward equatorial jets driven by wave and flow interactions. However, its connection with the global reorganisation of atmospheric energy transport remains less understood, particularly in Earth-like planetary atmospheres. In this work, we investigate superrotation from an energetic and transport-based perspective using a suite of three-dimensional global circulation model simulations of Earth-like planets performed with the THOR dynamical core.

We explore circulation behaviour across a broad range of planetary rotation rates and radiative timescales within a double-grey radiative transfer framework, focusing on the competition between meridional overturning transport and zonal redistribution of energy. By analysing global diagnostics of meridional and zonal transport, superrotation indices, and the relative contributions from mean circulation and eddies, we identify non-monotonic transitions between distinct transport regimes as rotational constraints become increasingly important.

Our results suggest that the atmospheric circulation initially increases its large-scale transport efficiency as the circulation becomes dynamically organised. However, the meridional overturning branch eventually reaches a maximum efficiency or loses effectiveness, after which the circulation increasingly reorganises toward zonal redistribution and strong equatorial jets. In this picture, superrotation emerges not simply as an isolated jet phenomenon, but as part of a broader atmospheric response to limitations in overturning-supported energy transport.

The rotation experiments reveal a clear transition between overturning-dominated and jet-supported transport regimes, with maximum zonal transport occurring at intermediate-to-slow rotation rates. In contrast, the radiative-adjustment scaling experiments do not exhibit a simple saturation of the equatorial jet, suggesting that the jet-supported transport branch can continue strengthening even after the overturning circulation becomes inefficient. Overall, our results support the idea that superrotation can be interpreted as a dynamically adaptive transport regime emerging from the reorganisation of atmospheric energy redistribution, while also highlighting the richer nonlinear behaviour present in fully three-dimensional radiative circulation models.