Recent Rate Constant and Product Measurements of the Reactions C2H3+ H2and C2H3+ H—Importance for Photochemical Modeling of Hydrocarbons on Jupiter

The structure of the Jovian stratosphere at the Galileo probe entry site is investigated through calculations of radiative heating rates based on measurements of the temperature profile, composition, and aerosol distribution. From analysis of mid-IR observations of Jupiter, we determine a C 2 H 2 mole fraction of 1.1-4.3 × 10 −6 at 0.01 mbar, and a C 2 H 6 mole fraction of 2.8-6.5 × 10 −6 at 0.4-10 mbar. The derived distributions imply that C 2 H 6 and C 2 H 2 are the most important coolants in the Jovian stratosphere from 0.004 to 10 mbar, and that the stratosphere is close to radiative equilibrium. In Jupiter's stratosphere, as in the stratosphere of the Earth, photochemical species play an essential role in the energy balance.

Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

Structure of the Jovian Stratosphere at the Galileo Probe Entry Site

Yelle

Griffith

Young

2001

“…While these values do change with both latitude and time , the assumed values of the NH 3 and PH 3 parameters have negligible effect in fitting the stratospheric emission features used in this study. For CH 4 , the vertical profile was based on a photochemical model by Romani (1996) but with a 5% increase in deep concentrations in order to match the results of Galileo's Neutral Mass Spectrometer experiment (Niemann et al, 1998 , which is representative of a mid-northern latitude region.…”

Section: Compositionmentioning

confidence: 99%

Jupiter’s auroral-related stratospheric heating and chemistry I: Analysis of Voyager-IRIS and Cassini-CIRS spectra

Sinclair

Orton

Greathouse

et al. 2017

107

Auroral processes are evident in Jupiter's polar atmosphere over a large range in wavelength (X-ray to radio). In particular, previous observations in the mid-infrared (5 to 15 µm) have shown enhanced emission from CH 4 , C 2 H 2 and C 2 H 4 and further stratospheric hydrocarbon species in spatial regions coincident with auroral processes observed at other wavelengths. These regions, described as auroral-related hotspots, observed at approximately 160• W to 200• W (System III) at high-northern latitudes and 330• W to 80• W at high-southern latitudes, indicate that auroral processes modify the thermal structure and composition of the neutral atmosphere. However, previous studies have struggled to differentiate whether the aforementioned enhanced emission is a result of either temperature changes and/or changes in the concentration of the emitting species. We attempt to address this degeneracy in this work by performing a retrieval analysis of Voyager 1-IRIS spectra (acquired in 1979) and Cassini-CIRS spectra (acquired in 2000/2001) of Jupiter. Retrievals of the vertical temperature profile in Cassini-CIRS spectra covering the auroral-related hotspots indicate the presence of two discrete vertical regions of heating at the 1-mbar level and at pressures of 10-µbar and lower. For example, in Cassini-CIRS 2.5 cm −1 'MIRMAP' spectra at 70• N (planetographic) 180• W (centred on the auroral oval), we find temperatures at the 1-mbar level and 10-µbar levels are enhanced by 15.3 ± 5.2 K and 29.6 ± 15.0 K respectively, in comparison to results at 70• N, 60• W in the same dataset. High temperatures at 10-µbar and lower pressures were considered indicative of joule heating, ion and/or electron precipitation, ion-drag and energy released form exothermic ion-chemistry. However, we conclude that the heating at the 1-mbar level is the result of either a layer of aurorally-produced haze particles, which are heated by incident sunlight and/or adiabatic heating by downwelling within the auroral hot-spot region. The former mechanism would be consistent with the vertical profiles of polycyclic aromatic hydrocarbons (PAHs) and haze particles predicted in auroral-chemistry models (Wong et al., 2000(Wong et al., , 2003. Retrievals of C 2 H 2 and C 2 H 6 were also performed and indicate C 2 H 2 is enriched but C 2 H 6 is depleted in auroral regions relative to quiescent regions. For example, using CIRS ∆ν = 2.5 cm −1 spectra, we determined that C 2 H 2 at 0.98 mbar increases by 175.3 ± 89.3 ppbv while C 2 H 6 at 4.7 mbar decreases by 0.86 ± 0.59 ppmv in comparing results at 70• N, 180• W and 70• N, 60• W. These results represent a mean of values retrieved from different initial assumptions and thus we believe they are robust. We believe these contrasts in C 2 H 2 and C 2 H 6 between auroral and quiescent regions can be explained by a coupling of auroral-driven chemistry and horizontal advection. Ion-neutral and electron recombination chemistry in the auroral region enriches all C 2 hydrocarbons but in particular, the unsaturated ...

“…However, alternative temperature profiles are also tested in performing retrievals. The vertical profiles of CH 4 and its isotopologues are adopted from Romani (1996) and the vertical profiles of all remaining hydrocarbons were assumed from the photochemical model by . Further details of the model atmosphere are provided in Section 3 of Sinclair et al (2017a).…”

Section: Radiative Transfer Modellingmentioning

confidence: 99%

Jupiter’s auroral-related stratospheric heating and chemistry II: Analysis of IRTF-TEXES spectra measured in December 2014

Sinclair

Orton

Greathouse

et al. 2018

We present a retrieval analysis of TEXES (Texas Echelon Cross Echelle Spectrograph (Lacy et al., 2002)) spectra of Jupiter's high latitudes obtained on NASA's Infrared Telescope Facility on December 10-11th 2014. The vertical temperature profile and vertical profiles of C 2 H 2 , C 2 H 4 and C 2 H 6 were retrieved at both high-northern and high-southern latitudes and results were compared in 'quiescent' regions and regions known to be affected by Jupiter's aurora in order to highlight how auroral processes modify the thermal structure and hydrocarbon chemistry of the stratosphere. In qualitative agreement with Sinclair et al. (2017a), we find temperatures in auroral regions to be elevated with respect to quiescent regions at two discrete pressures levels at approximately 1 mbar and 0.01 mbar. For example, in comparing retrieved temperatures at 70• N, 60• W (a representative quiescent region) and 70• N, 180• W (centred on the northern auroral oval), temperatures increase by 19.0 ± 4.2 K at 0.98 mbar, 20.8 ± 3.9 K at 0.01 mbar but only by 8.3 ± 4.9 K at the intermediate level of 0.1 mbar. We conclude that elevated temperatures at 0.01 mbar result from heating by joule resistance of the atmosphere and the energy imparted by electron and ion precipitation. However, temperatures at 1 mbar are considered to result either from heating by shortwave radiation of aurorally-produced haze particulates or precipitation of higher energy population of charged particles. Our former conclusion would be consistent with results of auroral-chemistry models, that predict the highest number densities of aurorally-produced haze particles at this pressure level (Wong et al., 2000(Wong et al., , 2003. C 2 H 2 and C 2 H 4 exhibit enrichments but C 2 H 6 remains constant within uncertainty when comparing retrieved concentrations in the northern auroral region with quiescent longitudes in the same latitude band. At 1 mbar, C 2 H 2 increases from 278.4 ± 40.3 ppbv at 70• N, 60• W to 564.4 ± 72.0 ppbv at 70• N, 180• W and at 0.01 mbar, over the same longitude range at 70• N, C 2 H 4 increases from 0.669 ± 0.129 ppmv to 6.509 ± 0.811 ppmv. However, we note that non-LTE (local thermodynamic equilibrium) emission may affect the cores of the strongest C 2 H 2 and C 2 H 4 lines on the northern auroral region, which may be a possible source of error in our derived concentrations. We retrieved concentrations of C 2 H 6 at 1 mbar of 9.03 ± 0.98 ppmv at 70• N, 60• W and 7.66 ± 0.70 ppmv at 70• N, 180• W. Thus, C 2 H 6 's concentration appears constant (within uncertainty) as a function of longitude at 70• N.