Observations of the temporal evolution of Saturn’s stratosphere following the Great Storm of 2010–2011

II. Latitudinal distribution of CO and stratospheric winds

¹ Univ. Bordeaux, CNRS, LAB, UMR 5804, 33600 Pessac, France
² LIRA – Laboratoire d’Instrumentation et de Recherche en Astrophysique, Observatoire de Paris, Section de Meudon, 5, place Jules Janssen, 92195 Meudon Cedex, France
³ Aix-Marseille Université, CNRS, CNES, Institut Origines, LAM, Marseille, France
⁴ Université de Reims Champagne-Ardenne, CNRS, GSMA, Reims, France
⁵ Planetary Atmospheres, Royal Belgian Institute for Space Aeronomy, Avenue Circulaire, 1180 Brussels, Belgium
⁶ Institute of Life, Earth and Environment (ILEE), University of Namur (UNamur), 61 rue de Bruxelles, Namur 5000, Belgium
⁷ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
⁸ Institut de Radioastronomie Millimétrique (IRAM), 38406 Saint-Martin-d’Hères, France
⁹ School of Physics and Astronomy, University of Leicester, Leicester, UK
¹⁰ Laboratoire de Météorologie Dynamique, Ecole Normale Supérieure, 24 rue Lhomond, 75231 Paris, France

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 29 August 2025
Accepted: 23 January 2026

Abstract

Context. Saturn’s Great Storm of 2010–2011 has produced two stratospheric hot spots, the “beacons,” that eventually merged to produce a gigantic one in April and May 2011. This beacon perturbed stratospheric temperatures, hydrocarbon, and water abundances for several years.

Aims. We aim to assess whether the beacon induced any perturbation in another oxygen species, namely CO. A second goal is to measure how the vortex perturbed the stratospheric wind regime.

Methods. We conducted interferometric observations of Saturn in the submillimeter range with SMA and ALMA to spatially resolve the CO (J=3–2) and (J=2–1) emissions, respectively. We used a previously determined CO vertical profile as a template, to search for (i) the meridional distribution of CO and (ii) variations of the CO abundance associated with the storm. The high spatial and spectral resolutions of the ALMA observations enabled us to retrieve the winds from the Doppler shifts induced by the winds on the lines.

Results. Despite limitations resulting from the removal of baseline ripples, we find a relatively constant meridional distribution of CO. The average CO mole fraction implied by the adopted and rescaled 220-year-old-comet-impact vertical profile is (1.7±0.7)×10⁻⁷ at 0.3 mbar, i.e., where the contribution functions peak. We also find that the CO abundance has not been noticeably altered in the beacon. The winds measured at 1 mbar show striking differences with those measured in 2018, after the demise of the beacon. We find the signature of the vortex as an anticyclonic feature. The equatorial prograde jet is 100–200 m s⁻¹ slower, and broader in latitude, than in quiescent conditions. We also detect several prograde jets in the southern hemisphere. Finally, we detect a retrograde jet at 74°N which could be a polar jet caused by the interaction of the Saturn magnetosphere with its atmosphere.

Conclusions. With Saturn’s equinox season approaching, new wind measurements would enable the findings presented in this paper to be confirmed by probing the two hemispheres equally and searching for a southern retrograde polar jet.