Traveling planetary-scale waves cause cloud variability on tidally locked aquaplanets
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Date
21/04/2023Author
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Abstract
Cloud cover at the planetary limb of water-rich Earth-like planets is likely to weaken chemical signatures in transmission spectra, impeding attempts to characterize these atmospheres. However, based on observations of Earth and Solar System worlds, exoplanets with atmospheres should have both short-term weather and long-term climate variability, implying that cloud cover may be less during some observing periods. We identify and describe a mechanism driving periodic clear sky events at the terminators in simulations of tidally locked Earth-like planets. A feedback between dayside cloud–radiative effects, incoming stellar radiation and heating, and the dynamical state of the atmosphere, especially the zonal wavenumber 1 Rossby wave identified in past work on tidally locked planets, leads to oscillations in Rossby wave phase speeds and in the position of Rossby gyres, and this results in advection of clouds to or away from the planet's eastern terminator. We study this oscillation in simulations of Proxima Centauri b, TRAPPIST-1e, and rapidly rotating versions of these worlds located at the inner edge of their stars' habitable zones. We simulate time series of the transit depths of the 1.4 μm water feature and 2.7 μm carbon dioxide feature. The impact of atmospheric variability on the transmission spectra is sensitive to the structure of the dayside cloud cover and the location of the Rossby gyres, but none of our simulations have variability significant enough to be detectable with current methods.
Citation
Cohen , M , Bollasina , M A , Sergeev , D E , Palmer , P I , Mayne , N J & Mayne , N J 2023 , ' Traveling planetary-scale waves cause cloud variability on tidally locked aquaplanets ' , The Planetary Science Journal , vol. 4 , no. 4 , 68 . https://doi.org/10.3847/PSJ/acc9c4
Publication
The Planetary Science Journal
Status
Peer reviewed
ISSN
2632-3338Type
Journal article
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© 2023. The Author(s). Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence (https://creativecommons.org/licenses/by/4.0/). Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Description
Funding: The authors acknowledge the funding and support provided by the Edinburgh Earth, Ecology, and Environmental Doctoral Training Partnership and the Natural Environment Research Council [grant No. NE/S007407/1]. We also kindly acknowledge our use of the Monsoon2 system, a collaborative facility supplied under the Joint Weather and Climate Research Programme, a strategic partnership between the Met Office and the Natural Environment Research Council. Our research was performed as part of the project "Using UKCA to investigate atmospheric composition on extra-solar planets" (ExoChem). This work was supported by a UKRI Future Leaders Fellowship [grant No. MR/T040866/1], Science and Technology Facilities Council Consolidated Grant [ST/R000395/1], and the Leverhulme Trust through a research project grant [RPG-2020-82].Collections
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