Exeter Exoplanet Theory Group

exoclimatology.com

Group leader: Nathan Mayne

Staff: Eric Hebrard, Hugo Lambert

Postdocs: Duncan Christie, Arwen Nicholson, Denis Sergeev, Maria Zamyatina

PhD students: Michelle Bieger, Jake Eager, Alex Loader, Robert Ridgway

IT support: Krisztian Kohary

UK Met Office collaborators:

• Ian Boutle
• James Manners
• Benjamin Drummond
• Stefan Lines

Adapted for extraterrestrial atmospheres!

UM for exoplanet atmospheres

• First adaptation of dynamical core: Mayne+ (2014a,b) 
• First adaptation of the radiative transfer (RT), and implementation of overlap scheme: Amundsen+ (2014, 2017) 
• First use of RT&dynamics for hot Jupiters: Amundsen+ (2016)
• First use of Gibbs minimisation chemical equilibrium scheme: Drummond+ (2018a)
• First use of chemical relaxation scheme: Drummond+ (2018b)
• First use of cloud model (DIHRT) for hot Jupiters: Lines+ (2018)
• First application of climate model (GA7.0) to rocky exoplanets: Boutle+ (2017)
• First use of land surface model: Lewis+ (2018)
• Exploring the role of mineral dust: Boutle+ (2020)
• Exploring the role of stellar spectra: Eager+ (2020)
• First use of the nesting suite: Sergeev+ (2020)

Motivation

Exoplanets

• >4000 exoplanets discovered
• Most detected are gas giants (like Jupiter)
• More rocky planets are detected too

... are awesome!

Tidally locked exoplanets

• Habitable ~ have surface liquid water 
• M-dwarf are relatively cool stars
• Potentially habitable planets around M-dwarfs have to orbit closer to their host stars
• Strong tidal forces
• Planet can become tidally locked
• Orbital period = rotation period
• Permanent day-side and night-side

Climate of Earth-like tidally locked exoplanets

Climate of Earth-like tidally locked exoplanets

Climate of Earth-like tidally locked exoplanets

Challenges in convection modelling

• Wide scale separation between convection and planetary-scale circulation 
• Convection is subgrid-scale and parameterised
• All existing parameterisations are tested against observations on Earth
• No in-situ measurements on exoplanets

Modelling setup

and global climate simulations

• Orbital parameters of Trappist-1e and Proxima Centauri b
• Planets are tidally locked to M-dwarf stars
• \(N_2\)-dominated atmosphere with traces of \(CO_2\) and \(H_2O\)
• Mean surface pressure of 1 bar
• Aquaplanet regime (a slab ocean)
• Two modes
  • Global coarse-resolution (\(2^\circ\times 2.5^\circ\)) model with parameterised convection
  • Regional high-resolution (4 km) model with explicit convection

Credit: NASA/JPL-Caltech

Credit: ESA

Global simulation of Trappist-1e

Shown are:

• Surface temperature
• Cloud condensate
• Upper troposphere wind vectors

The effects of convection parameterisation on global simulations

• "MassFlux" (Gregory-Rowntree) vs "Adjust" (Lambert-Lewis) convection schemes
• The global climate of TL exoplanets is altered (and not just the day side!)
• The effect is planet-dependent: the climate regime on Trappist-1e is more sensitive
• More detailed analysis of these runs is given in Sergeev+ (2020)

Surface temperature (\(T_s\)), and

free-troposphere winds

Trappist-1e

Proxima b

High-resolution simulations

"global" (MassFlux)

"HighRes"

RA-1T setup

Spatial variability: top-of-atmosphere outgoing LW radiation

Spatial variability: top-of-atmosphere outgoing LW radiation

Spatial variability: top-of-atmosphere outgoing LW radiation

Spatial variability: top-of-atmosphere outgoing LW radiation

Histograms of instantaneous TOA OLR

Spatial variability: top-of-atmosphere outgoing LW radiation

Histograms of instantaneous TOA OLR

Vertical cloud structure (averaged profiles)

Vertical cloud structure (averaged profiles)

Vertical cloud structure (averaged profiles)

Latent heating (averaged profiles)

Global impact of resolved convection

• Caveat: one-way nesting of the model
• How to assess the impact of HighRes simulations on the global climate?

• Caveat: one-way nesting of the model
• How to assess the impact of HighRes simulations on the global climate?

1. Run an ensemble of global experiments with perturbed convection parameters

1. Run an ensemble of global experiments with perturbed convection parameters
2. Integrate a metric of convection strength over the substellar region

• Caveat: one-way nesting of the model
• How to assess the impact of HighRes simulations on the global climate?

1. Run an ensemble of global experiments with perturbed convection parameters
2. Integrate a metric of convection strength over the substellar region
3. Correlate with a metric of day-night heat redistribution

• Caveat: one-way nesting of the model
• How to assess the impact of HighRes simulations on the global climate?

1. Run an ensemble of global experiments with perturbed convection parameters
2. Integrate a metric of convection strength over the substellar region
3. Correlate with a metric of day-night heat redistribution
4. Extrapolate for the convection metric from HighRes simulations

• Caveat: one-way nesting of the model
• How to assess the impact of HighRes simulations on the global climate?

1. Run an ensemble of global experiments with perturbed convection parameters
2. Integrate a metric of convection strength over the substellar region
3. Correlate with a metric of day-night heat redistribution
4. Extrapolate for the convection metric from HighRes simulations

• Caveat: one-way nesting of the model
• How to assess the impact of HighRes simulations on the global climate?

1. Run an ensemble of global experiments with perturbed convection parameters
2. Integrate a metric of convection strength over the substellar region
3. Correlate with a metric of day-night heat redistribution
4. Extrapolate for the convection metric from HighRes simulations

• Caveat: one-way nesting of the model
• How to assess the impact of HighRes simulations on the global climate?

Summary

• Representation of convection is important for the global climate of exoplanets
• The sensitivity to convection scheme is planet-dependent
• Global UM is biased in the cloud structure and cloud radiative feedbacks w.r.t. to HighRes
• A hypothetical global convection-permitting simulation may enhance the day-night temperature contrast
• Valuable cases for idealised convection modelling, providing "stress-tests" for the UM