Please use this identifier to cite or link to this item: http://hdl.handle.net/2381/38783
Title: Jupiter's Para-H2 Distribution from SOFIA/FORCAST and Voyager/IRIS 17-37 µm Spectroscopy
Authors: Fletcher, Leigh N.
de Pater, I.
Reach, W. T.
Wong, M.
Orton, G.
Irwin, P. G. J.
Gehrz, R. D.
First Published: 6-Oct-2016
Publisher: Elsevier for Academic Press
Citation: Icarus 2016
Abstract: Spatially resolved maps of Jupiter’s far-infrared 17–37 µm hydrogen-helium collision-induced spectrum were acquired by the FORCAST instrument on the Stratospheric Observatory for Infrared Astronomy (SOFIA) in May 2014. Spectral scans in two grisms covered the broad S(0) and S(1) absorption lines, in addition to contextual imaging in eight broad-band filters (5–37 µm) with spatial resolutions of 2–4″. The spectra were inverted to map the zonal-mean temperature and para-H2 distribution (fp, the fraction of the para spin isomer with respect to the ortho spin isomer) in Jupiter’s upper troposphere (the 100–700 mbar range). We compared these to a reanalysis of Voyager-1 and -2 IRIS spectra covering the same spectral range. Tropospheric temperature contrasts match those identified by Voyager in 1979, within the limits of temporal variability consistent with previous investigations. Para-H2 increases from equator to pole, with low-fp air at the equator representing sub-equilibrium conditions (i.e., less para-H2 than expected from thermal equilibration), and high-fp air and possible super-equilibrium at higher latitudes. In particular, we confirm the continued presence of a region of high-fp air at high northern latitudes discovered by Voyager/IRIS, and an asymmetry with generally higher fp in the north than in the south. Far-IR aerosol opacity is not required to fit the data, but cannot be completely ruled out. We note that existing collision-induced absorption databases lack opacity from (H2)2 dimers, leading to under-prediction of the absorption near the S(0) and S(1) peaks. There appears to be no spatial correlation between para-H2 and tropospheric ammonia, phosphine and cloud opacity derived from Voyager/IRIS at mid-infrared wavelengths (7–15 µm). We note, however, that para-H2 tracks the similar latitudinal distribution of aerosols within Jupiter’s upper tropospheric and stratospheric hazes observed in reflected sunlight, suggesting that catalysis of hydrogen equilibration within the hazes (and not the main clouds) may govern the equator-to-pole gradient, with conditions closer to equilibrium at higher latitudes. This gradient is superimposed onto smaller-scale variations associated with regional advection of para-H2 at the equator and poles.
DOI Link: 10.1016/j.icarus.2016.10.002
ISSN: 0019-1035
Links: http://www.sciencedirect.com/science/article/pii/S0019103516301269
http://hdl.handle.net/2381/38783
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: © 2016 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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