ClimaTea Lecture: "The 0.1 bar Tropopause Rule"

Speaker: Tyler Robinson (NASA Fellow)

Abstract:

Tropopause temperature minima are fundamental for understanding planetary atmospheric structure.  A number of shortwave absorbers (e.g., ozone, organic hazes) produce temperature inversions in the stratospheres of Earth, Jupiter, Saturn, Titan, Uranus and Neptune.  These inversions lead to temperature minima that, remarkably, all occur near 0.1 bar, despite very different insolation, atmospheric composition, gravity, and internal heat flux.  Using simple models, we find that, for the worlds of the solar system, the tropopause temperature minimum always lies above the radiative-convective boundary, and occurs at a preferred value of the gray infrared optical depth.  Thus, the shared 0.1 bar tropopause arises from the common physics of infrared radiative transfer.  Moving beyond the solar system, we discuss how the tropopause temperature minimum may be at 0.1 bar for a very wide range of plausible atmospheric compositions, and what this means for the characterization of exoplanets.