To identify promising exoplanets for atmospheric characterization and to make
the best use of observational data, a thorough understanding of their
atmospheres is needed. 3D general circulation models (GCMs) are one of the most
comprehensive tools available for this task and will be used to interpret
observations of temperate rocky ...
To identify promising exoplanets for atmospheric characterization and to make
the best use of observational data, a thorough understanding of their
atmospheres is needed. 3D general circulation models (GCMs) are one of the most
comprehensive tools available for this task and will be used to interpret
observations of temperate rocky exoplanets. Due to various parameterization
choices made in GCMs, they can produce different results, even for the same
planet. Employing four widely-used exoplanetary GCMs -- ExoCAM, LMD-Generic,
ROCKE-3D and the UM -- we continue the TRAPPIST-1 Habitable Atmosphere
Intercomparison by modeling aquaplanet climates of TRAPPIST-1e with a moist
atmosphere dominated by either nitrogen or carbon dioxide. Although the GCMs
disagree on the details of the simulated regimes, they all predict a temperate
climate with neither of the two cases pushed out of the habitable state.
Nevertheless, the inter-model spread in the global mean surface temperature is
non-negligible: 14 K and 24 K in the nitrogen and carbon dioxide dominated
case, respectively. We find substantial inter-model differences in moist
variables, with the smallest amount of clouds in LMD-Generic and the largest in
ROCKE-3D. ExoCAM predicts the warmest climate for both cases and thus has the
highest water vapor content, the largest amount and variability of cloud
condensate. The UM tends to produce colder conditions, especially in the
nitrogen-dominated case due to a strong negative cloud radiative effect on the
day side of TRAPPIST-1e. Our study highlights various biases of GCMs and
emphasizes the importance of not relying solely on one model to understand
exoplanet climates.