TRAPPIST-1

Bistability Of The Atmospheric Circulation On TRAPPIST-1e

By Keith Cowing
astro-ph.EP
July 25, 2022
Filed under
Bistability Of The Atmospheric Circulation On TRAPPIST-1e
The mean climate diagnostics in all experiments: (a) maximum equatorial zonal wind speed (x-axis, m s−1 ) and the latitude of the tropospheric jet (y-axis, degrees); (b) the ratio of the day-night to equator-pole temperature difference (x-axis) and the minimum surface temperature (y-axis, K). Experiments that produce the SJ regime are shown in blue, DJ — in orange. Different marker shapes correspond to different groups of sensitivity experiments. Configuration labels are defined in Table 2. Also shown is the steady state of the (c) SJ and (d) DJ circulation regimes in the indicative simulations (Base and T0 280, respectively). Panels c and d show the vertical cross-section of the zonal mean eastward wind (shading, m s−1 ) and zonal mean air temperature (contours, K). Horizontal dashed lines in c and d show the corresponding pressure level of the horizontal cross-sections of (red) temperature and (gray) winds and geopotential height shown in Fig. 7. “Single Jet” (SJ) and “Double Jet” (DJ) are short-hand descriptive terms rather than precise descriptions: the equatorial jet in the SJ regime exhibits a split at σ ≈ 0.5, and the DJ regime still has an equatorial superrotation, albeit weaker than that in the SJ regime.

Using a 3D general circulation model, we demonstrate that a confirmed rocky exoplanet and a primary observational target, TRAPPIST-1e presents an interesting case of climate bistability.

We find that the atmospheric circulation on TRAPPIST-1e can exist in two distinct regimes for a 1~bar nitrogen-dominated atmosphere. One is characterized by a single strong equatorial prograde jet and a large day-night temperature difference; the other is characterized by a pair of mid-latitude prograde jets and a relatively small day-night contrast. The circulation regime appears to be highly sensitive to the model setup, including initial and surface boundary conditions, as well as physical parameterizations of convection and cloud radiative effects.

We focus on the emergence of the atmospheric circulation during the early stages of simulations and show that the regime bistability is associated with a delicate balance between the zonally asymmetric heating, mean overturning circulation, and mid-latitude baroclinic instability. The relative strength of these processes places the GCM simulations on different branches of the evolution of atmospheric dynamics.

The resulting steady states of the two regimes have consistent differences in the amount of water content and clouds, affecting the water absorption bands as well as the continuum level in the transmission spectrum, although they are too small to be detected with current technology. Nevertheless, this regime bistability affects the surface temperature, especially on the night side of the planet, and presents an interesting case for understanding atmospheric dynamics and highlights uncertainty in 3D GCM results, motivating more multi-model studies.

Denis E. Sergeev, Neil T. Lewis, F. Hugo Lambert, Nathan J. Mayne, Ian A. Boutle, James Manners, Krisztian Kohary

Comments: 31 pages, 14 figures, accepted to the Planetary Science Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Atmospheric and Oceanic Physics (physics.ao-ph)
Cite as: arXiv:2207.12342 [astro-ph.EP] (or arXiv:2207.12342v1 [astro-ph.EP] for this version)
Submission history
From: Denis Sergeev
[v1] Mon, 25 Jul 2022 16:58:42 UTC (5,845 KB)
https://arxiv.org/abs/2207.12342
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