Cloud behaviour on tidally locked rocky planets from global high-resolution modelling

Yang, Jun; Zhang, Yixiao; Fu, Zuntao; Yan, Mingyu; Song, Xinyi; Wei, Mengyu; Liu, Jiachen; Ding, Feng; Tan, Zhihong

doi:10.1038/s41550-023-02015-8

Cited by 11 publications

(16 citation statements)

References 48 publications

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“…Such a scenario for K2-18b is not implausible: it has been demonstrated that rocky planets with water oceans may potentially maintain stable surface water inside of the inner edge of the habitable zone due to climate feedbacks of substellar clouds, provided that they are sufficiently slowly rotating planets (Yang et al 2013(Yang et al , 2023Way & Del Genio 2020). The Hycean scenario, however, may not be possible under the hot starting conditions from which the planet would evolve (Chachan & Stevenson 2018;Vazan et al 2018aVazan et al , 2018bKite & Barnett 2020;Kimura & Ikoma 2022).…”

Section: Ocean or Magma Ocean?mentioning

confidence: 99%

Distinguishing Oceans of Water from Magma on Mini-Neptune K2-18b

Shorttle,

Jordan,

Nicholls

et al. 2024

ApJL

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Mildly irradiated mini-Neptunes have densities potentially consistent with them hosting substantial liquid-water oceans (“Hycean” planets). The presence of CO2 and simultaneous absence of ammonia (NH3) in their atmospheres has been proposed as a fingerprint of such worlds. JWST observations of K2-18b, the archetypal Hycean, have found the presence of CO2 and the depletion of NH3 to <100 ppm; hence, it has been inferred that this planet may host liquid-water oceans. In contrast, climate modeling suggests that many of these mini-Neptunes, including K2-18b, may likely be too hot to host liquid water. We propose a solution to this discrepancy between observation and climate modeling by investigating the effect of a magma ocean on the atmospheric chemistry of mini-Neptunes. We demonstrate that atmospheric NH3 depletion is a natural consequence of the high solubility of nitrogen species in magma at reducing conditions; precisely the conditions prevailing where a thick hydrogen envelope is in communication with a molten planetary surface. The magma ocean model reproduces the present JWST spectrum of K2-18b to ≲3σ, suggesting this is as credible an explanation for current observations as the planet hosting a liquid-water ocean. Spectral areas that could be used to rule out the magma ocean model include the >4 μm region, where CO2 and CO features dominate: magma ocean models suggest a systematically lower CO2/CO ratio than estimated from free-chemistry retrieval, indicating that deeper observations of this spectral region may be able to distinguish between oceans of liquid water and magma on mini-Neptunes.

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Section: Ocean or Magma Ocean?mentioning

confidence: 99%

Distinguishing Oceans of Water from Magma on Mini-Neptune K2-18b

Shorttle,

Jordan,

Nicholls

et al. 2024

ApJL

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“…In addition to being coarse in horizontal resolution, our simulations use the hydrostatic primitive equations and thus would not be convection-permitting even at higher resolutions. Future work is needed to study the potential for tropical cyclogenesis in higher-resolution models of tidally locked terrestrial planets, including local convection-resolving large eddy simulations (Lefèvre et al 2021), global convectionresolving simulations (Yang et al 2023), or global simulations with nested grids (Sergeev et al 2020). Such work would facilitate a comparison between coarse global tropical cyclonepermitting simulations and tropical cyclone-resolving and convection-permitting simulations in order to determine the extent to which the methods used in this work are broadly applicable to study tropical cyclogenesis on tidally locked terrestrial exoplanets.…”

Section: Limitations and Future Workmentioning

confidence: 99%

Tropical Cyclones on Tidally Locked Rocky Planets: Dependence on Rotation Period

Garcia,

Smith,

Chavas

et al. 2024

ApJ

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Tropical cyclones occur over the Earth’s tropical oceans, with characteristic genesis regions and tracks tied to the warm ocean surface that provide energy to sustain these storms. The study of tropical cyclogenesis and evolution on Earth has led to the development of environmental favorability metrics that predict the strength of potential storms from the local background climate state. Simulations of the gamut of transiting terrestrial exoplanets orbiting late-type stars may offer a test of this Earth-based understanding of tropical cyclogenesis. Previous work has demonstrated that tropical cyclones are likely to form on tidally locked terrestrial exoplanets with intermediate rotation periods of ∼8–10 days. In this study, we test these expectations using ExoCAM simulations with both a sufficient horizontal resolution of 0.°47 × 0.°63 required to permit tropical cyclogenesis along with a thermodynamically active slab ocean. We conduct simulations of tidally locked and ocean-covered Earth-sized planets orbiting late-type M dwarf stars with varying rotation periods from 4–16 days in order to cross the predicted maximum in tropical cyclogenesis. We track tropical cyclones that form in each simulation and assess their location of maximum wind, evolution, and maximum wind speeds. We compare the resulting tropical cyclone locations and strengths to predictions based on environmental favorability metrics, finding good agreement between Earth-based metrics and our simulated storms with a local maximum in both tropical cyclone frequency and intensity at a rotation period of 8 days. Our results suggest that environmental favorability metrics used for tropical cyclones on Earth may also be applicable to temperate tidally locked Earth-sized rocky exoplanets with abundant surface liquid water.

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“…Noting that all models simulate more cloud ice than cloud liquid water, except CAM (Figure S3 in Supporting Information ), this may be associated with different temperature limits for the formation of ice/liquid cloud and different liquid‐ice partitioning schemes used in different models (Braun et al., 2022; Yang et al., 2023).…”

Section: Comparisons With Previous Simulationsmentioning

confidence: 99%

Fine Cloud Structures on a Hard Snowball Earth

Yan,

Yang

2024

JGR Atmospheres

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Earth may have been globally ice‐covered at least two times during the Cryogenian Period (720–635 Ma). Previous studies showed that clouds could strongly warm a hard snowball Earth and promote its deglaciation. However, the understanding of clouds was largely based on coarse‐resolution global simulations with parameterized convection and clouds, or high‐resolution cloud‐resolving simulations with explicit convection and clouds but limited to a small domain without the effects of large‐scale circulation. Here we present the first global non‐hydrostatic high‐resolution (30 km) simulation to investigate snowball clouds and their radiative effects. We show that spatial‐temporal cloud distributions exhibit clear meanders (patterns of curved lines rather than straight lines along the west‐east direction) and strong variabilities, which result from the tight interactions among the Inter‐Tropical Convergence Zone, Hadley cells, and baroclinic instability. The net cloud radiative effect is around 20 W m−2 in the tropics, consistent with previous global general circulation model simulations.

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Cloud behaviour on tidally locked rocky planets from global high-resolution modelling

Cited by 11 publications

References 48 publications

Distinguishing Oceans of Water from Magma on Mini-Neptune K2-18b

Distinguishing Oceans of Water from Magma on Mini-Neptune K2-18b

Tropical Cyclones on Tidally Locked Rocky Planets: Dependence on Rotation Period

Fine Cloud Structures on a Hard Snowball Earth

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