Traveling planetary-scale waves cause cloud variability on tidally locked aquaplanets by Maureen Cohen et al. on Wednesday 23 November

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 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 1-e, and rapidly rotating versions

of these worlds located at the extreme inner edge of their stars' habitable

zones. We simulate time series of the transit depths of the 1.4 {\mu}m water

feature and 2.7 {\mu}m 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.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.11887v1