Spatial Variations in the Altitude of the CH4 Homopause at Jupiter’s Mid-to-high Latitudes, as Constrained from IRTF-TEXES Spectra

Abstract

Abstract We present an analysis of IRTF-TEXES spectra of Jupiter’s mid-to-high latitudes in order to test the hypothesis that the CH4 homopause altitude is higher in Jupiter’s auroral regions compared to elsewhere on the planet. A family of photochemical models, based on Moses & Poppe (2017), were computed with a range of CH4 homopause altitudes. Adopting each model in turn, the observed TEXES spectra of H2 S(1), CH4, and CH3 emission measured on 2019 April 16 and August 20 were inverted, the vertical temperature profile was allowed to vary, and the quality of the fit to the spectra 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 homopause altitude lower than ∼360 km (above 1 bar). At 62°N, inside the main auroral oval, we derived a CH4 homopause altitude of km, whereas outside the main oval at the same latitude, a 1σ upper limit of 370 km was derived. Our interpretation is that a portion of energy from the magnetosphere is deposited as heat within the main oval, which drives vertical winds and/or higher rates of turbulence and transports CH4 and its photochemical by-products to higher altitudes. Inside the northern main auroral oval, a factor of ∼3 increase in CH3 abundance was also required to fit the spectra. This could be due to uncertainties in the photochemical modeling or an additional source of CH3 production in Jupiter’s auroral regions.