A076-03
Constraints on the height of the CH4 homopause from an analysis of IRTF-TEXES spectra

Wednesday, 9 December 2020: 16:06
Virtual
James Andrew Sinclair1, Thomas K Greathouse2, Rohini Giles3, Arrate Antuñano4, Julianne I Moses5, Thierry Fouchet6, Bruno Bezard7, George B Clark8, Chihiro Tao9, Denis C Grodent10, Glenn Orton11, Vincent Hue2, Leigh N. Fletcher12 and Patrick GJ Irwin13, (1)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (2)Southwest Research Institute, San Antonio, TX, United States, (3)Southwest Research Institute, San Antonio, United States, (4)University of Leicester, Leicester, LE1, United Kingdom, (5)Space Science Institute, Seabrook, TX, United States, (6)LESIA, Observatoire de Paris, Meudon, France, (7)Paris Observatory Meudon, Meudon, France, (8)Johns Hopkins University Applied Physics Laboratory, Laurel, MD, United States, (9)IRAP, Toulouse, France, (10)Université de Liège, LPAP - STAR Institute, Liege, Belgium, (11)Jet Propulsion Laboratory, Pasadena, CA, United States, (12)University of Leicester, Leicester, United Kingdom, (13)University of Oxford, Oxford, United Kingdom
Abstract:
We present an analysis of high-resolution spectra of Jupiter’s CH3 (methyl radical) and CH4 emission measured at mid-to-high latitudes with the goal of determining spatial and temporal variations in the altitude of the CH4 homopause. IRTF-TEXES (Texas Echelon Cross Echelle Spectrograph, Lacy et al., 2002, PASP 114, 153-168) spectra were measured on April 16th and August 20th 2019 and were inverted as follows. A family of photochemical models, based on Moses & Poppe (2017, Icarus 297, 33-58), was computed by varying the eddy diffusion coefficient in the upper stratosphere and thereby increasing the altitude of the CH4 homopause. Adopting each photochemical model in turn, the emission features of CH3 and CH4 were modeled simultaneously by allowing the vertical temperature profile to vary, and the quality of fit to the observations was used to discriminate between models. In preliminary results of August 20th 2019 spectra, we find that a CH4 homopause altitude below ~350 km (with respect to 1 bar) is required to fit the observations equatorward of the main oval. At 68°N, 180°W (planetocentric, System III), the center of the northern auroral region, a homopause altitude of ~450 km optimized the fit to the spectra. At 68°N, but sampling longitudes outside the main oval, a homopause altitude between ~336 km and ~400 km was required to fit the spectra. Our results confirm the hypothesis presented in previous work (e.g. Clark et al., 2018, JGR 123, 7554-7567) that the CH4 homopause altitude is higher in Jupiter’s auroral regions compared to elsewhere on the planet. This suggests deposition of energy from the magnetosphere drives turbulence and vertical winds, which advects CH4 and its photochemical by-products to higher altitudes. We will repeat this analysis for IRTF/TEXES and SOFIA/EXES observations scheduled near-contemporaneously with Juno’s 29th perijove (September 16th 2020) and search for temporal variations between measurements.
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