Global flow regimes of hot Jupiters

¹ Center for Space and Habitability, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
² Universitäts-Sternwarte München, Fakultät für Physik der Ludwig-Maximilians-Universität, Scheinerstraße 1, 81679 München, Deutschland
³ ARTORG Center for Biomedical Engineering Research, University of Bern, Murtenstrasse 50, 3008 Bern, Switzerland
⁴ University College London, Department of Physics & Astronomy, Gower St, London WC1E 6BT, UK
⁵ Astronomy & Astrophysics Group, Department of Physics, University of Warwick, Coventry CV4 7AL, UK
⁶ Department of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK
⁷ School of Ocean and Earth Science, University of Southampton, Southampton SO14 3ZH, UK
⁸ Canadian Centre for Climate Modelling and Analysis, Environment and Climate Change Canada, Victoria, BC, Canada
⁹ School of Earth and Ocean Sciences, University of Victoria, Victoria, BC, Canada

^★ Corresponding author.

Received: 23 December 2024
Accepted: 16 May 2025

Abstract

Context. The atmospheric dynamics of hot and ultrahot Jupiters are influenced by the stellar irradiation they receive, which shapes their atmospheric circulation and the underlying wave structures.

Aims. We aim to investigate how variations in radiative and dynamical timescales influence global flow regimes, atmospheric circulation efficiency, and the interplay of wave structures across a curated sample of hot Jupiters. In particular, we explore a previously predicted transition in the global flow regime, where enhanced stellar irradiation suppresses the smaller-scale wave and eddy features that feed into superrotating jets and ultimately leads to simpler, day-to-night dominated flows.

Methods. We simulated a suite of eight well-studied hot Jupiters with the THOR general circulation model, spanning equilibrium temperatures from about 1100 K to 2400 K. We developed a wavelet-based analysis method to decompose simulated wind fields into their underlying wave modes, which we validated on analytical examples. As a preliminary exploration of the flow regime of ultrahot Jupiters, we performed an additional simulation for WASP-121b, where the mean molecular weight was set to represent an atmosphere dominated by atomic hydrogen.

Results. Our results confirm that increasing stellar irradiation diminishes the efficiency of atmospheric heat redistribution and weakens the contribution of smaller-scale eddy modes critical for sustaining superrotation. As equilibrium temperatures rise, large-scale modes dominate the atmospheric circulation, driving a transition from jet-dominated flows toward day-to-night circulation. Additionally, by artificially lowering the mean molecular weight, we partially restore circulation efficiency and reintroduce a more complex, multiscale flow pattern. These findings refine our understanding of how atmospheric circulation evolves with increasing irradiation and composition changes, offering a more nuanced framework for interpreting hot and ultrahot Jupiter atmospheres.