Simulations and Observations of Uranus and Neptune atmospheric Dynamics – SOUND

Our main approach lies on the development of atmospheric models for these planets:
- On a large scale, by developing a general circulation model (GCM) based on an existing model on Jupiter and Saturn. It aims to study the thermal structure, the winds and the large-scale circulation and their forcings (waves, radiative forcing...) over the seasons;
- On a small scale by developing a variant of this model which solves the small-scale convective processes (not solved by the GCM mesh) in order to better understand the organization and the intermittency of the stormy activity on these planets.
- We also conduct an analysis of observations in the millimeter and sub-millimeter range in order to obtain new information on winds and temperature.

Thus this project combines approaches of modeling in climate sciences and astrophysical observations.

These three approaches are not independent because it is also about making comparisons between observations and model outputs, and links between small and large scale processes.

1. The development of the GCM of Uranus and Neptune is well advanced. A publication is in progress to document the evolution of the thermal structure over the seasons in the absence of dynamic forcing. Complete simulations (radiative and dynamical forcing) at 1° resolution have been performed and are under analysis.

2. The small-scale convection model has been developed for Neptune, including methane transport and condensation, and the first tests are very promising: convective plumes are forming at regular intervals.

3. Analyses of old ALMA observations are underway to constrain the stratospheric winds and temperature of Neptune.

We continue to try to obtain observing time on ALMA and NOEMA to improve the existing observations.

The GCM simulations of Uranus and Neptune will soon be analyzed in details (role of waves in the wind forcing; influence of seasons,...).

Several results have been presented at international conferences (EPSC 2021 and 2022).

There is a renewed interest in studying Uranus and Neptune's atmospheres in the scientific community as 1) they are considered to be archetypes of most exoplanets discovered so far and 2) sending a mission to either or both these planets is seriously considered by NASA and ESA within the 2028-2032 launch window. However, despite many observational studies, their atmospheric circulation remains poorly known. Here we propose to build a new, 3D General Circulation Model of these atmospheres to investigate their wind regime, characterized by strong zonal jets. In parallel, we will develop another model at finer scales that will resolve convective plumes, in order to study the intermittent storm activity on these planets. In addition to contribute to interpreting existing and future observations, we aim at understanding similarities and differences in atmospheric dynamics among the four giants planets, based on our expertise in modeling Saturn and Jupiter. Finally, the analysis of (sub)millimeter observations will allow us to measure, for the first time, stratospheric zonal wind speeds.