Experiments with the Extraterrestrial CRM Suite#

We will now run a couple of simulations using the u-dz791 suite. This suite is designed to model convection in hydrogen-rich atmospheres of other planets in a highly simplified setup - the default configuration uses only the dynamical core (GungHo).

Key features#

  • The dynamical core only. All parameterizations are switched off.

  • No rotation.

  • Hydrogen-dominated atmosphere. In the dynamics-only setup this is controlled via the gas constants: isobaric heat capacity cp=14300 and the dry gas constant rd=4124.00.

  • Initial temperature profile: isothermal (uses a branch for a corrected procedure - see dependencies.yaml).

  • Initial vapour profile: step-wise profile with more vapour in the upper atmosphere to sustain compositional convection.

  • Initial wind profile: zero.

Science motivation#

In the context of hydrogen-rich atmospheres, we are particularly keen to explore how convection works in a presence of a compositional gradient, e.g. a large vertical gradient of water vapour.

Why is this interesting?

Beyond Earth, a particularly interesting case is moist convection in hydrogen-dominated atmospheres. Unlike on Earth, where the mean molecular weight of the background gas surpasses that of water vapour, hydrogen-dominated atmospheres exhibit a stabilising molecular-weight gradient, as the condensable has a greater mean molecular weight than that of the background gas (Ledoux, 1947). Consequently, in atmospheres with non-dilute amounts of the condensable (>10% by mass; see e.g. Pierrehumbert & Ding, 2016), the background temperature gradient can no longer be solely relied on to predict convective stability. This effect is not as important for convection on Earth since water vapour only contributes up to a few percent by mass, hence lying comfortably in the dilute regime.

Suggested experiments#

The following practical exercises are suggested to explore the idealised setup further. You will need to use what you learned in the running and navigating exercises to edit and run the experiments. For analysis, you can use what you learnt in the visualisation exercises.

Contents

Example from previous studies: changing the water vapour profile

Habib & Pierrehumbert (2024) use another cloud-resolving model and find that destabilizing mean molecular weight gradients can lead to compositional convection in otherwise thermally stable atmospheres. They test this using high-resolution non-condensing simulations for a range of background compositions and thermal profiles. LFRic allows us to repeat their experiments by changing the background composition (gas constants) and the initial profile of water vapour. Talk to Alex Corbett if you are interested.

Note

If you decide to test your own experiment with a code or configuration change, be ready to do lots of debugging! If you want an example which is tried and tested, use the suggested examples above.