Assessing the long-term variability of acetylene and ethane in the stratosphere of Jupiter

Abstract

Acetylene (C${}_2$H${}_2$) and ethane (C${}_2$H${}_6$) are both produced in the stratosphere of Jupiter via photolysis of methane (CH${}_4$). Despite this common source, the latitudinal distribution of the two species is radically different, with acetylene decreasing in abundance towards the pole, and ethane increasing towards the pole. We present six years of NASA IRTF TEXES mid-infrared observations of the zonally-averaged emission of methane, acetylene and ethane. We confirm that the latitudinal distributions of ethane and acetylene are decoupled, and that this is a persistent feature over multiple years. The acetylene distribution falls off towards the pole, peaking at $\sim$30${}^{\circ }$N with a volume mixing ratio (VMR) of $\sim$0.8 parts per million (ppm) at 1 mbar and still falling off at $\pm 70^{\circ }$ with a VMR of $\sim$0.3 ppm. The acetylene distributions are asymmetric on average, but as we move from 2013 to 2017, the zonally-averaged abundance becomes more symmetric about the equator. We suggest that both the short term changes in acetylene and its latitudinal asymmetry is driven by changes to the vertical stratospheric mixing, potentially related to propagating wave phenomena. Unlike acetylene, ethane has a symmetric distribution about the equator that increases toward the pole, with a peak mole fraction of $\sim$18 ppm at about $\pm 50^{\circ }$ latitude, with a minimum at the equator of $\sim$10 ppm at 1 mbar. [...] The equator-to-pole distributions of acetylene and ethane are consistent with acetylene having a shorter lifetime than ethane that is not sensitive to longer advective timescales, but is augmented by short-term dynamics, such as vertical mixing. Conversely, the long lifetime of ethane allows it to be transported to higher latitudes faster than it can be chemically depleted.

39 pages, 9 Figures, 2 tables, in press

References in corpus (3)

• The Origin of Nitrogen on Jupiter and Saturn from the ${}^{15}$N/${}^{14}$N Ratio
• Jupiter's North Equatorial Belt expansion and thermal wave activity ahead of Juno's arrival
• Cycles of Activity in the Jovian Atmosphere

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• Jupiter in the ultraviolet: acetylene and ethane abundances in the stratosphere of Jupiter from Cassini observations between 0.15 and 0.19 $\mu$m
• Meridional variations of C${}_2$H${}_2$ in Jupiter's stratosphere from Juno UVS observations
• Enhanced C${}_2$H${}_2$ absorption within Jupiter's southern auroral oval from Juno UVS observations
• Mid-Infrared Observations of the Giant Planets
• The Polar Stratosphere of Jupiter
• A retrospective analysis of mid-infrared observations of the Comet D/Shoemaker-Levy 9 and Wesley impacts on Jupiter
• Microphysical Model of Jupiter's Great Red Spot Upper Chromophore Haze
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• Giant Planet Atmospheres