Topography-Induced Stationary Waves and the Onset of Nightside Warming on Rocky Planets around M-dwarf Stars

Abstract

Among potentially habitable worlds, rocky planets orbiting M dwarfs offer the most favorable prospects for atmospheric characterization, yet their climates may differ substantially from those of Earth analogs. In the tidally locked limit, the nightside's tendency to radiatively cool and potentially trap volatiles as permanent ice introduces a strong dependence of habitability on the planet's surface and atmospheric boundary conditions. We perform a suite of synchronously rotating experiments spanning a wide range of topographic and orographic realizations with different mean elevations and landmass distributions. Across a grid of $p_{N2}=0.5$-$8\mathrm{bar}$ and $F_{\star }=1200$-$1700\mathrm{W}{\mathrm{m}}^{-2}$, we find that surface relief breaks the flow symmetry, replacing the circumpolar vortices with mechanically forced stationary waves. Steep orography produces standing Rossby gyres that strengthen the cross-terminator jet and align vertical uplift with the day--night boundary. These new circulation regimes enhance moisture transport, increasing the infrared optical depth and promoting additional nightside cloud formation, which produces a stronger cloud-greenhouse feedback and lower the critical fluxes required for global planetary deglaciation. Broad, elevated plateaus drive a similarly fragmented but slightly weaker circulation, yielding less effective moisture transport. These results show that the relief and spatial distribution of landmasses, parameters unconstrained for most exoplanets, can exert strong controls on the climatic bifurcations of tidally locked M-dwarf exoplanets.

15 pages, 11 figures, 1 table; accepted to ApJ; comments welcome prior to final proofs

References in corpus (13)

• Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1
• The habitability of Proxima Centauri b II. Possible climates and Observability
• Atmospheric dynamics of Earth-like tidally locked aquaplanets
• Atmospheric dynamics of terrestrial exoplanets over a wide range of orbital and atmospheric parameters
• Ocean Dynamics and the Inner Edge of the Habitable Zone for Tidally Locked Terrestrial Planets
• The distribution of volatile elements during rocky planet formation
• The Effect of Substellar Continent Size on Ocean Dynamics of Proxima Centauri b
• A 1.55 R${}_{\oplus }$ habitable-zone planet hosted by TOI-715, an M4 star near the ecliptic South Pole
• Variability due to climate and chemistry in observations of oxygenated Earth-analogue exoplanets
• Land Fraction Diversity on Earth-like Planets and Implications for their Habitability
• Diversity of low-mass planet atmospheres in the C-H-O-N-S-Cl system with interior dissolution, nonideality, and condensation: Application to TRAPPIST-1e and sub-Neptunes
• Water versus land on temperate rocky planets
• Born Dry or Born Wet? A Palette of Water Growth Histories in TRAPPIST-1 Analogs and Compact Planetary Systems