Multiple Climate States of Habitable Exoplanets: The Role of Obliquity and Irradiance

Kilic, Cevahir; Raible, Christoph; Stocker, Thomas (2017). Multiple Climate States of Habitable Exoplanets: The Role of Obliquity and Irradiance. Astrophysical journal, 844(2), p. 147. Institute of Physics Publishing IOP 10.3847/1538-4357/aa7a03

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Stable, steady climate states on an Earth-size planet with no continents are determined as a function of the tilt of the planet's rotation axis (obliquity) and stellar irradiance. Using a general circulation model of the atmosphere coupled to a slab ocean and a thermodynamic sea ice model, two states, the Aquaplanet and the Cryoplanet, are found for high and low stellar irradiance, respectively. In addition, four stable states with seasonally and perennially open water are discovered if comprehensively exploring a parameter space of obliquity from 0° to 90° and stellar irradiance from 70% to 135% of the present-day solar constant. Within 11% of today's solar irradiance, we find a rich structure of stable states that extends the area of habitability considerably. For the same set of parameters, different stable states result if simulations are initialized from an aquaplanet or a cryoplanet state. This demonstrates the possibility of multiple equilibria, hysteresis, and potentially rapid climate change in response to small changes in the orbital parameters. The dynamics of the atmosphere of an aquaplanet or a cryoplanet state is investigated for similar values of obliquity and stellar irradiance. The atmospheric circulation substantially differs in the two states owing to the relative strength of the primary drivers of the meridional transport of heat and momentum. At 90° obliquity and present-day solar constant, the atmospheric dynamics of an Aquaplanet state and one with an equatorial ice cover is analyzed.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Physics Institute > Climate and Environmental Physics
10 Strategic Research Centers > Oeschger Centre for Climate Change Research (OCCR)
10 Strategic Research Centers > Center for Space and Habitability (CSH)

UniBE Contributor:

Kilic, Cevahir; Raible, Christoph and Stocker, Thomas

Subjects:

500 Science > 530 Physics
500 Science > 520 Astronomy

ISSN:

0004-637X

Publisher:

Institute of Physics Publishing IOP

Language:

English

Submitter:

Doris Rätz

Date Deposited:

22 Nov 2017 10:42

Last Modified:

14 Mar 2018 15:32

Publisher DOI:

10.3847/1538-4357/aa7a03

BORIS DOI:

10.7892/boris.106535

URI:

https://boris.unibe.ch/id/eprint/106535

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