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Mapping of Jupiter’s tropospheric NH3 abundance using ground-based IRTF/TEXES observations at 5 µm

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posted on 25.06.2019, 10:50 by D Blain, T Fouchet, T Greathouse, T Encrenaz, B Charnay, B Bezard, C Li, E Lellouch, G Orton, LN Fletcher, P Drossart
We report on results of an observing campaign to support the Juno mission. At the beginning of 2016, using TEXES (Texas Echelon cross-dispersed Echelle Spectrograph), mounted on the NASA Infrared Telescope Facility (IRTF), we obtained data cubes of Jupiter in the 1930–1943 cm−1 spectral ranges (around 5 µm), which probe the atmosphere in the 1–4 bar region, with a spectral resolution of ≈ 0.15 cm−1 and an angular resolution of ≈ 1.4”. This dataset is analysed by a code that combines a line-by-line radiative transfer model with a non-linear optimal estimation inversion method. The inversion retrieves the vertical abundance profiles of NH3 — which is the main contributor at these wavelengths — with a maximum sensitivity at ≈ 1–3 bar, as well as the cloud transmittance. This retrieval is performed on more than one thousand pixels of our data cubes, producing maps of the disk, where all the major belts are visible. We present our retrieved NH3 abundance maps which can be compared with the distribution observed by Juno’s MWR (Bolton et al., 2017; Li et al., 2017) in the 2 bar region and discuss their significance for the understanding of Jupiter’s atmospheric dynamics. We are able to show important latitudinal variations — such as in the North Equatorial Belt (NEB), where the NH3 abundance is observed to drop down to 60 ppmv at 2 bar — as well as longitudinal variability. In the zones, we find the NH3 abundance to increase with depth, from 100 ± 15 ppmv at 1 bar to 500 ± 30 ppmv at 3 bar. We also display the cloud transmittance–NH3 abundance relationship, and find different behaviour for the NEB, the other belts and the zones. Using a simple cloud model (Lacis and Hansen, 1974; Ackerman and Marley, 2001), we are able to fit this relationship, at least in the NEB, including either NH3-ice or NH4SH particles with sizes between 10 and 100 µm


D.B. and T.F. were supported by the Programme National de Planétologie as well as the Centre National d’Etudes Spatiales. T.G. acknowledges funding supporting this work from NASA PAST through grant number NNH12ZDAO01N-PAST. G.S.O. was supported by funds from the National Aeronautics and Space Administration distributed to the Jet Propulsion Laboratory, California Institute of Technology. Fletcher was supported by a Royal Society Research Fellowship at the University of Leicester.



Icarus, 2018, 314, pp. 106-120 (15)

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/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy


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Supplementary material associated with this article can be found, in the online version, at doi: 10.1016/j.icarus.2018.06.002