Regime transition between eddy-driven and moist-driven circulation on High Obliquity Planets

TL;DR

This study explores how high obliquity planets transition between eddy-driven and moist-driven circulations, revealing regime shifts influenced by insolation and rotation rate, with observable atmospheric signatures.

Contribution

It introduces a decomposition of planetary circulation into diabatic and adiabatic components, highlighting how obliquity affects circulation regimes and their observable signatures.

Findings

Diabatic processes dominate low obliquity circulation.

High obliquity shows a transition from adiabatic to diabatic dominance.

Momentum-driven circulation resembles dry model dynamics under high obliquity.

Abstract

We investigate how the meridional circulation and baroclinic eddies change with insolation and rotation rate, under high and zero obliquity setups, using a general circulation model. The total circulation is considered as superposition of circulations driven by different physics processes, such as diabatic and adiabatic processes. We decompose the meridional circulation into diabatic and adiabatic components, in order to understand their different responses to changes of insolation and rotation rate. As insolation or rotation period increases, the meridional circulation tends to become more diabatically dominant, regardless of the obliquity. The low obliquity circulation is always dominated by diabatic processes, while the high obliquity configuration has two circulation regimes: an adiabatic-dominant regime in the limit of low insolation and fast rotation, and a diabatic-dominant regime in the opposite limit. This regime transition may be observable via its signature on the upper atmospheric zonal wind and the column cloud cover. The momentum-driven circulation, the dominant circulation component in the weak-insolation and fast-rotating regimes is found to resemble that in a dry dynamic model forced by a reversed meridional temperature gradient, indicating the relevance of using a dry dynamic model to understand planetary general circulations under high obliquity.