Spatial variations in the CH4 homopause altitude at Jupiter’s mid-to-high latitudes

The polar atmosphere of Jupiter is strongly influenced by the external magnetosphere and interplane-
tary environment. Previous studies have inferred that the CH4 homopause, which denotes the level
where eddy and molecular diffusion coefficients are equal, is higher in altitude inside Jupiter’s main
auroral ovals compared to elsewhere on the planet (e.g. Parkinson et al., 2006, JGRE 111, Gustin
et al., 2016, 268, Clark et al., 2018, JGRA 123). The exact altitude of the CH4 homopause is poorly
constrained at Jupiter’s high latitudes and is currently a large source of uncertainty in the analyses
of Jupiter’s ultraviolet auroral emissions, which are being measured regularly by Juno, Hisaki and
Hubble. We present an analysis of IRTF-TEXES (Texas Echelon Cross Echelle Spectrograph, Lacy et al.,
2002 PASP 114) spectra of Jupiter’s mid-to-high latitudes in order to constrain the CH4 homopause
altitude and its spatial variation. The spectral emission features of H2 S(1), CH3 and CH4 emission were
measured on April 16th and August 20th 2019. The spectra were inverted using a family of atmo-
spheric models with varying CH4 homopause altitudes, and the goodness-of-fit to the observations
was used to discriminate between models. At latitudes equatorward of Jupiter’s main auroral ovals
(>62◦S, <54◦N, planetocentric), the observations were adequately fit assuming a CH4 homopause
altitude lower than 360 km above 1 bar. At 62◦N, using a mean of observations measured within the
main oval, we derived a CH homopause altitude of 461+147 km. At the same latitude, but sampling 4 −39
longitudes outside the main oval, we derive a homopause altitude of 331 km, with a 1-σ upper limit of 370 km. Thus, we confirm the CH4 homopause altitude is 70 - 130 km higher in Jupiter’s auroral regions compared to elsewhere on the planet. This would suggest the deposition of energy from the magnetosphere ultimately drives vertical winds and/or turbulence, which transports CH4 and its photochemical byproducts to higher altitudes. We found no evidence of statistically-significant spatial or temporal variability of the homopause altitude within the main oval however this may be a sampling artefact. We will also present preliminary analyses of IRTF-TEXES observations to be measured on June 28-29 and compare with previous TEXES measurements in order to search for temporal variability.