Joint evolution of equatorial oscillation and interhemispheric circulation in Saturn’s stratosphere

Deborah Bardet (1) , Aymeric Spiga (1) , Sandrine Guerlet (1, 2)

1 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)
2 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique = Laboratory of Space Studies and Instrumentation in Astrophysics

Planetary stratospheres are characterized by a subtle interplay between dynamics, radiation, and chemistry. Observations of Saturn's stratosphere revealed a semi-annual equatorial oscillation of temperature and hinted at an inter-hemispheric circulation of hydrocarbon species. Both the forcing mechanisms of the former and the existence of the latter have remained debated. Here we use a new troposphere-to-stratosphere Saturn global climate model to argue that those two open questions are intimately connected. Our Saturn climate model reproduces a stratospheric oscillation exhibiting the observed semi-annual period, amplitude, and downward propagation. In the same Saturn simulation, a prominent stratospheric summer-to-winter hemispheric circulation develops at solstices, controlled by both the seasonal radiative gradients and Rossby-wave pumping in the winter subsiding branch, analogous to Earth's Brewer-Dobson circulation. Furthermore, we show that Saturn's equatorial oscillation is driven by the seasonal variability of both the resolved planetary-scale wave activity and the inter-hemispheric circulation, akin to Earth's Semi-Annual Oscillation.

Domaines: Planète et Univers [physics]; Océan, Atmosphère; Planétologie et astrophysique de la terre [astro-ph.EP]

Deborah Bardet, Aymeric Spiga, Sandrine Guerlet. Joint evolution of equatorial oscillation and interhemispheric circulation in Saturn’s stratosphere. Nature Astronomy, 2022, ⟨10.1038/s41550-022-01670-7⟩. ⟨hal-03690475⟩