Impact of methane abundance on storm formation on Uranus & Neptune, revealed by a cloud-resolving model

Despite the weak solar flux received by the ice giant planets, the storm activity of their atmospheres is intense. What is then the phenomenon responsible for this activity?

On Uranus and Neptune, a notable property draws attention: unlike the Earth, the species able to condense in the atmospheres of ice giants, methane in particular, are heavier than the ambient air, essentially hydrogen. This property makes convection difficult to start.

Convection in these atmospheres should therefore be a regime of strong intermittence where convective energy can be stored for a long time before being released in short episodes.

Our hypothesis is that this regime is at the origin of intense storms.

To study this hypothesis, we use a "cloud-resolving" model. This model is built from a dynamical core (The Weather Research and Forecasting model) solving the equations of motion, that has been initially developed for terrestrial applications and already adapted for simulations on Mars and Venus, coupled to independent physical parameterizations such as radiative transfer and micro-physics. The high resolution of the model grid can allow us to highlight moist atmospheric convection, by resolving cloud formation and dissipation.

Having successfully implemented the methane cycle in this model, we will present results from our 3D simulations, which reveal the impact of the methane cycle in tropospheric convection on Uranus & Neptune, having a special look at the methane abundance, that vary at different latitudes, and how it affects storms frequencies and intensities.