Habitable Zones & Global Climate

Stratosphere Circulation On Tidally Locked ExoEarths

By Keith Cowing
Press Release
November 30, 2017
Filed under
Stratosphere Circulation On Tidally Locked ExoEarths

Stratosphere circulation is important to interpret abundances of photo-chemically produced compounds like ozone that we aim to observe to assess habitability of exoplanets.

We thus investigate a tidally locked ExoEarth scenario for TRAPPIST-1b, TRAPPIST-1d, Proxima Centauri~b and GJ 667 C~f with a simplified 3D atmosphere model and for different stratospheric wind breaking assumptions.

These planets are representatives for different circulation regimes for orbital periods: Porb=1−100~days. The circulation of exoplanets with Porb≤ 25~days can be dominated by the standing tropical Rossby wave in the troposphere and also in the stratosphere: It leads to a strong equatorial eastward wind jet and to ‘Anti-Brewer-Dobson’-circulation that confines air masses to the stratospheric equatorial region. Thus, the distribution of photo-chemically produced species and aerosols may be limited to an ‘equatorial transport belt’. In contrast, planets with Porb>25~days, like GJ~667~C~f, exhibit efficient thermally driven circulation in the stratosphere that allows for a day side-wide distribution of air masses.

The influence of the standing tropical Rossby waves on tidally locked ExoEarths with Porb≤25~days can, however, be circumvented with deep stratospheric wind breaking alone – allowing for equator-to-pole transport like on Earth. For planets with 3≤Porb≤6~days, the extratropical Rossby wave acts as an additional safe-guard against the tropical Rossby wave in case of shallow wind breaking. Therefore, TRAPPIST-1d is less prone to have an equatorial transport belt in the stratosphere than Proxima~Centauri~b.
Even our Earth model shows an equatorial wind jet, if stratosphere wind breaking is inefficient.

Ludmila Carone, Rony Keppens, Leen Decin, Thomas Henning
(Submitted on 29 Nov 2017)

Comments: 14 pages, 13 figures
Subjects: Atmospheric and Oceanic Physics (physics.ao-ph); Earth and Planetary Astrophysics (astro-ph.EP); Space Physics (physics.space-ph)
Journal reference: Monthly Notices of the Royal Astronomical Society, Volume 473, Issue 4, 1 February 2018, Pages 4672 – 4685
DOI: 10.1093/mnras/stx2732
Cite as: arXiv:1711.11446 [physics.ao-ph] (or arXiv:1711.11446v1 [physics.ao-ph] for this version)
Submission history
From: Ludmila Carone
[v1] Wed, 29 Nov 2017 15:02:57 GMT (4466kb)

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