loading page

What is the Altitude of Thermal Equilibrium?
  • +3
  • William K. Peterson,
  • Naomi Maruyama,
  • Phil G. Richards,
  • Philip J Erickson,
  • Andrew B Christensen,
  • Andrew Yau
William K. Peterson
University of Colorado Boulder

Corresponding Author:[email protected]

Author Profile
Naomi Maruyama
University of Colorado
Author Profile
Phil G. Richards
George Mason University
Author Profile
Philip J Erickson
Massachusetts Institute of Technology
Author Profile
Andrew B Christensen
Dixie State University
Author Profile
Andrew Yau
University of Calgary
Author Profile


Thermal equilibrium in planetary atmospheres occurs at altitudes where the ion, electron, and neutral temperatures are equal. Thermal equilibrium is postulated to occur in the collision-dominated lower ionosphere. This postulated altitude is above the lower boundary of all empirical models of planetary ionospheres. Physics-based model predictions of the altitude can not be validated due to a lack of adequate simultaneous observations of temperature profiles. This study presents temperature profiles from simultaneous observations on Atmosphere Explorer–C below 140 km and quiet-time neutral observations from TIMED/GUVI over Millstone Hill. These are compared with profiles from physics-based models with a discussion of their respective limitations. We conclude that there does not yet exist a quantitative understanding of the ion, electron, and neutral thermalization processes in low-altitude planetary ionospheres. Progress on this topic requires an adequate database of simultaneous ion, electron, and temperature profiles in the 110 to 140 km altitude range.
10 Jan 2023Submitted to ESS Open Archive
17 Jan 2023Published in ESS Open Archive
16 Jun 2023Published in Geophysical Research Letters volume 50 issue 11. 10.1029/2023GL102758