Modelling H${}_3^{+}$ in planetary atmospheres: effects of vertical gradients on observed quantities

Abstract

Since its discovery in the aurorae of Jupiter ~30 years ago, the H${}_3^{+}$ ion has served as an invaluable probe of giant planet upper atmospheres. However, the vast majority of monitoring of planetary H${}_3^{+}$ radiation has followed from observations that rely on deriving parameters from column-integrated paths through the emitting layer. Here, we investigate the effects of density and temperature gradients along such paths on the measured H${}_3^{+}$ spectrum and its resulting interpretation. In a non-isothermal atmosphere, H${}_3^{+}$ column densities retrieved from such observations are found to represent a lower limit, reduced by 20% or more from the true atmospheric value. Global simulations of Uranus' ionosphere reveal that measured H${}_3^{+}$ temperature variations are often attributable to well-understood solar zenith angle effects rather than indications of real atmospheric variability. Finally, based on these insights, a preliminary method of deriving vertical temperature structure is demonstrated at Jupiter using model reproductions of electron density and H${}_3^{+}$ measurements. The sheer diversity and uncertainty of conditions in planetary atmospheres prohibits this work from providing blanket quantitative correction factors; nonetheless, we illustrate a few simple ways in which the already formidable utility of H${}_3^{+}$ observations in understanding planetary atmospheres can be enhanced.

arXiv comment14 pages, 9 figures, part of Philosophical Transactions A special issue following workshop entitled "Advances in hydrogen molecular ions: H3+, H5+ and beyond"

References in corpus (4)

• Dust Ablation on the Giant Planets: Consequences for Stratospheric Photochemistry
• First submillimeter observation of CO in the stratosphere of Uranus
• Mid-Infrared Spectroscopy of Uranus from the Spitzer Infrared Spectrometer: 2. Determination of the Mean Composition of the Upper Troposphere and Stratosphere
• The quest for H${}_3^{+}$ at Neptune: deep burn observations with NASA IRTF iSHELL

Cited by in corpus (5)

• Atmospheric chemistry on Uranus and Neptune
• The Galactic cosmic ray intensity at the evolving Earth and young exoplanets
• Spatiotemporal Variations of Temperature in Jupiter's Upper Atmosphere
• Ionospheric conductances at the giant planets of the Solar System:a comparative study of ionization sources and the impact of meteoric ions
• Chaos Gated Tunneling Drives Molecular Reactivity in Astrophysical Environments