Common 0.1 bar tropopause in thick atmospheres determined by pressure-dependent infrared transparency (Nature Geoscience, 2013)

• David Catling
• Tyler Robinson

Full Citation:
Robinson, T., Catling, D. Common 0.1 bar tropopause in thick atmospheres set by pressure-dependent infrared transparency. Nature Geosci 7, 12–15 (2014). https://doi.org/10.1038/ngeo2020

Abstract:
A minimum atmospheric temperature, or tropopause, occurs at a pressure of around 0.1 bar in the atmospheres of Earth1, Titan2, Jupiter3, Saturn4, Uranus and Neptune4, despite great differences in atmospheric composition, gravity, internal heat and sunlight. In all of these bodies, the tropopause separates a stratosphere with a temperature profile that is controlled by the absorption of short-wave solar radiation, from a region below characterized by convection, weather and clouds5,6. However, it is not obvious why the tropopause occurs at the specific pressure near 0.1 bar. Here we use a simple, physically based model7 to demonstrate that, at atmospheric pressures lower than 0.1 bar, transparency to thermal radiation allows short-wave heating to dominate, creating a stratosphere. At higher pressures, atmospheres become opaque to thermal radiation, causing temperatures to increase with depth and convection to ensue. A common dependence of infrared opacity on pressure, arising from the shared physics of molecular absorption, sets the 0.1 bar tropopause. We reason that a tropopause at a pressure of approximately 0.1 bar is characteristic of many thick atmospheres, including exoplanets and exomoons in our galaxy and beyond. Judicious use of this rule could help constrain the atmospheric structure, and thus the surface environments and habitability, of exoplanets.

URL:
https://www.nature.com/articles/ngeo2020

VPL Research Tasks:
Task C: The Habitable Planet