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

Melin, Henrik; Fletcher, Leigh N.; Donnelly, Padraig T.; Greathouse, T. K.; Lacy, J. H.; Orton, Glenn S.; Giles, Rohini; Sinclair, James; Irwin, Patrick G. J.

doi:10.1016/j.icarus.2017.12.041

Cited by 31 publications

(58 citation statements)

References 34 publications

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“…However, the Cassini observations indicate that both molecules have an opposite behavior: while the C 2 H 2 abundance globally decreases with latitude, the abundance of C 2 H 6 increases with latitude. This trend was recently confirmed with a large set of ground based observations, showing that its feature is stable over time (Melin et al, 2018).…”

Section: Introductionsupporting

confidence: 55%

Photochemistry, mixing and transport in Jupiter’s stratosphere constrained by Cassini

Hue

Hersant

Cavalié

et al. 2018

Icarus

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In this work, we aim at constraining the diffusive and advective transport processes in Jupiter's stratosphere, using Cassini/CIRS observations published by Nixon et al. (2007Nixon et al. ( , 2010. The Cassini-Huygens flyby of Jupiter on December 2000 provided the highest spatially resolved IR observations of Jupiter so far, with the CIRS instrument. The IR spectrum contains the fingerprints of several atmospheric constituents and allows probing the tropospheric and stratospheric composition. In particular, the abundances of C 2 H 2 and C 2 H 6 , the main compounds produced by methane photochemistry, can be retrieved as a function of latitude in the pressure range at which CIRS is sensitive to. CIRS observations suggest a very different meridional distribution for these two species. This is difficult to reconcile with their photochemical histories, which are thought to be tightly coupled to the methane photolysis. While the overall abundance of C 2 H 2 decreases with latitude, C 2 H 6 becomes more abundant at high latitudes. In this work, a new 2D (latitude-altitude) seasonal photochemical model of Jupiter is developed. The model is used to investigate whether the addition of stratospheric transport processes, such as meridional diffusion and advection, are able to explain the latitudinal behavior of C 2 H 2 and C 2 H 6 . We find that the C 2 H 2 observations are fairly well reproduced without meridional diffusion. Adding meridional diffusion to the model provides an improved agreement with the C 2 H 6 observations by flattening its meridional distribution, at the cost of a degradation of the fit to the C 2 H 2 distribution. However, meridional diffusion alone cannot produce the observed increase with latitude of the C 2 H 6 abundance. When adding 2D advective transport between roughly 30 mbar and 0.01 mbar, with upwelling winds at the equator and downwelling winds at high latitudes, we can, for the first time, reproduce the C 2 H 6 abundance increase with latitude. In parallel, the fit to the C 2 H 2 distribution is degraded. The strength of the advective winds needed to reproduce the C 2 H 6 abundances is particularly sensitive to the value of the meridional eddy diffusion coefficient. The coupled fate of these methane photolysis by-products suggests that an additional process is missing in the model. Ion-neutral chemistry was not accounted for in this work and might be a good candidate to solve this issue. 1

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Section: Introductionsupporting

confidence: 55%

Photochemistry, mixing and transport in Jupiter’s stratosphere constrained by Cassini

Hue

Hersant

Cavalié

et al. 2018

Icarus

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“…Having explored the potentially multi-tiered circulation cells in the upper troposphere and mid-troposphere, we now turn our attention to atmospheric motions above the tropopause. On the Gas Giants, the zonal winds and banded structures persist high into the stratosphere, and are superimposed onto larger interhemispheric circulations, both non-seasonal on Jupiter (Nixon et al 2007;Zhang et al 2013;Melin et al 2018) and seasonal on Saturn (see review by . The temperature and composition of the Gas Giant stratospheres is also modulated by the presence of polar vortices and wave-driven equatorial oscillations.…”

Section: Stratospheric Circulation: Chemical Tracersmentioning

confidence: 99%

Ice Giant Circulation Patterns: Implications for Atmospheric Probes

et al. 2020

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Atmospheric circulation patterns derived from multi-spectral remote sensing can serve as a guide for choosing a suitable entry location for a future in situ probe mission to the Ice Giants. Since the Voyager-2 flybys in the 1980s, three decades of observations from ground- and space-based observatories have generated a picture of Ice Giant circulation that is complex, perplexing, and altogether unlike that seen on the Gas Giants. This review seeks to reconcile the various competing circulation patterns from an observational perspective, accounting for spatially-resolved measurements of: zonal albedo contrasts and banded appearances; cloud-tracked zonal winds; temperature and para-H2 measurements above the condensate clouds; and equator-to-pole contrasts in condensable volatiles (methane, ammonia, and hydrogen sulphide) in the deeper troposphere. These observations identify three distinct latitude domains: an equatorial domain of deep upwelling and upper-tropospheric subsidence, potentially bounded by peaks in the retrograde zonal jet and analogous to Jovian cyclonic belts; a mid-latitude transitional domain of upper-tropospheric upwelling, vigorous cloud activity, analogous to Jovian anticyclonic zones; and a polar domain of strong subsidence, volatile depletion, and small-scale (and potentially seasonally-variable) convective activity. Taken together, the multi-wavelength observations suggest a tiered structure of stacked circulation cells (at least two in the troposphere and one in the stratosphere), potentially separated in the vertical by (i) strong molecular weight gradients associated with cloud condensation, and by (ii) transitions from a thermally-direct circulation regime at depth to a wave- and radiative-driven circulation regime at high altitude. The inferred circulation can be tested in the coming decade by 3D numerical simulations of the atmosphere, and by observations from future world-class facilities. The carrier spacecraft for any probe entry mission must ultimately carry a suite of remote-sensing instruments capable of fully constraining the atmospheric motions at the probe descent location.

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“…The TEXES instrument (Texas Echelon Cross Echelle Spectrograph, Lacy et al, 2002) has proven to be a powerful means of characterising the atmospheric temperatures, composition, and aerosols on Jupiter during the Juno mission (Fletcher, Greathouse, et al, 2016;Cosentino et al, 2017;Melin et al, 2018;Blain et al, 2018). This cross-dispersed grating spectrograph provides spatially-resolved spectral maps in specially selected channels from the M band (5 µm), to the N band (7-13 µm), and the Q band (17-24 µm).…”

Section: Gemini Texesmentioning

confidence: 99%

“…This typically requires 50-80% reductions in the calibrated TEXES brightness (e.g., see Fig. 8 of Fletcher, Greathouse, et al, 2016), and is a known and repeatable feature of TEXES calibration in low-and medium-resolution settings, where the detectors exhibit non-linear behaviour as a function of brightness (Melin et al, 2018). The largest changes were found in the middle of the N-band near 10 µm (1000 cm −1 ), where the TEXES data had to be reduced by 7.8-9.3 K (in terms of brightness temperature).…”

Section: Zonal Mean Inversionsmentioning

confidence: 99%

“…The largest changes were found in the middle of the N-band near 10 µm (1000 cm −1 ), where the TEXES data had to be reduced by 7.8-9.3 K (in terms of brightness temperature). Note that, following Melin et al (2018), we do not adjust the measured radiances in the 1248 cm −1 channel. The CIRS reference model of Fletcher, Greathouse, et al (2016) has been updated in this work in an attempt to find consistency with the zonally-averaged NH 3 profiles derived from MWR data acquired during PJ1 (27 August 2016) by Li et al (2017) -full details are given in Appendix B.…”

Section: Zonal Mean Inversionsmentioning

confidence: 99%

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Jupiter's Equatorial Plumes and Hot Spots: Spectral Mapping from Gemini/TEXES and Juno/MWR

Orton¹,

Grassi²,

Levin³

et al. 2020

Preprint

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Key Points:• Gemini TEXES spectral mapping reveals temperature, aerosol, and ammonia contrasts associated with plumes and hot spots on Jupiter's NEB jetstream. • Juno microwave measurements are consistent with the infrared mapping, and reveals that hot spot ammonia contrasts are confined to pressures less than 8-10 bars. • Hot spots and plumes are primarily contrasts in aerosols, with only subtle uppertropospheric ammonia and temperature variations. AbstractWe present multi-wavelength measurements of the thermal, chemical, and cloud contrasts associated with the visibly dark formations (also known as 5-µm hot spots) and intervening bright plumes on the boundary between Jupiter's Equatorial Zone (EZ) and North Equatorial Belt (NEB). Observations made by the TEXES 5-20 µm spectrometer at the Gemini North Telescope in March 2017 reveal the upper-tropospheric properties of 12 hot spots, which are directly compared to measurements by Juno using the Microwave Radiometer (MWR), JIRAM at 5 µm, and JunoCam visible images. MWR and thermal-infrared spectroscopic results are consistent near 0.7 bar. Midinfrared-derived aerosol opacity is consistent with that inferred from visible-albedo and 5-µm opacity maps. Aerosol contrasts, the defining characteristics of the cloudy plumes and aerosol-depleted hot spots, are not a good proxy for microwave brightness. The hot spots are neither uniformly warmer nor ammonia-depleted compared to their surroundings at p < 1 bar. At 0.7 bar, the microwave brightness at the edges of hot spots is comparable to other features within the NEB. Conversely, hot spots are brighter at 1.5 bar, signifying either warm temperatures and/or depleted NH 3 at depth. Temperatures and ammonia are spatially variable within the hot spots, so the precise location of the observations matters to their interpretation. Reflective plumes sometimes have enhanced NH 3 , cold temperatures, and elevated aerosol opacity, but each plume appears different. Neither plumes nor hot spots had microwave signatures in channels sensing p > 10 bars, suggesting that the hot-spot/plume wave is a relatively shallow feature. Plain Language SummaryTo date, our only direct measurement of Jupiter's gaseous composition came from the descent of the Galileo probe in 1995. However, the results from Galileo appeared to be biased due to the unusual meteorological conditions of its entry location: a dark, cloud-free region just north of the equator, known as a hot spot. One of the aims of NASA's Juno mission was to place the findings of the Galileo probe into broader context, which requires a detailed characterisation of these equatorial hot spots and their neighbouring plumes. We combine (a) data from Juno (microwave observations sounding conditions below the clouds, and visible/infrared observations revealing variations in cloud opacity) with (b) observations from amateur observers (to track the hot spots over time) and (c) observations from the TEXES infrared spectrometer mounted on the Gemini-North telescope. The latter provides the highest-re...

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

Cited by 31 publications

References 34 publications

Photochemistry, mixing and transport in Jupiter’s stratosphere constrained by Cassini

Photochemistry, mixing and transport in Jupiter’s stratosphere constrained by Cassini

Ice Giant Circulation Patterns: Implications for Atmospheric Probes

Jupiter's Equatorial Plumes and Hot Spots: Spectral Mapping from Gemini/TEXES and Juno/MWR

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