Latitudinal and seasonal models of stratospheric photochemistry on Saturn: Comparison with infrared data from IRTF/TEXES
Abstract
The variation of hydrocarbon abundances with altitude, latitude, and season in Saturn's stratosphere is investigated using a one‐dimensional, time‐variable, photochemical model. The results indicate that hydrocarbon abundances at pressures less than ∼0.01 mbar are extremely sensitive to solar flux variations due to changes in season, latitude, orbital radius, solar cycle, and ring shadowing. Long vertical diffusion times in the 0.01–1 mbar region introduce phase lags in the response to insolation changes. At pressures greater than 1 mbar, vertical diffusion timescales are longer than a Saturnian year. Therefore, relatively long‐lived hydrocarbons like C 2 H 2, C 2 H 6, and C 3 H 8 exhibit little seasonal variation in the lower stratosphere, and the yearly averaged solar insolation combined with vertical diffusion control species abundances in this region. Species with short photochemical lifetimes (e.g., CH 3, C 2 H 4) continue to experience seasonal variations, even at low altitudes. The model results are compared with infrared observations from the TEXES spectrometer at NASA's Infrared Telescope Facility. We find that the observed C 2 H 2 mixing‐ratio variation with latitude is reasonably well predicted, whereas the C 2 H 6 distribution is poorly predicted by the models. Meridional transport is likely affecting the distribution of C 2 H 6, which has a long photochemical lifetime, whereas the distribution of shorter‐lived C 2 H 2 is controlled by photochemistry and vertical diffusion. Given the different observed behavior of C 2 H 2 and C 2 H 6, we constrain meridional transport timescales at 2 mbar on Saturn to be in the range ∼100–700 years, corresponding to meridional wind or diffusion speeds of ∼0.4–2 cm s−1.
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The primary stratospheric coolants ethane and acetylene are spatially and temporally variable due to photochemistry and atmospheric circulation.
“In particular, the primary stratospheric coolants (ethane and acetylene) are spatially and temporally variable due to both photochemistry and atmospheric circulation18–24”
From A hexagon in Saturn's northern stratosphere surrounding the emerging summertime polar vortex (2018) · cites this paper as [18]
There is a weak trend with photochemical species longevity: longer-lived ethane and propane show the most similarity between poles (ratios 0.7-1.0), while shorter-lived acetylene, diacetylene and methyl acetylene show greater contrasts (0.2-0.6).
“There may be a weak trend with the longevity of the photochemical species18, with longer-lived ethane and propane showing the most similarity between the poles (ratios of 0.7–1.0) and the shorter-lived acetylene, diacetylene and methyl acetylene showing greater contrasts (0.2–0.6).”
From A hexagon in Saturn's northern stratosphere surrounding the emerging summertime polar vortex (2018) · cites this paper as [18]
Cites
Saturn's Temperature Field from High-Resolution Middle-Infrared Imaging
Orton, G. S., & Yanamandra-Fisher, P. A. (2005) · Science · doi:10.1126/science.1105730 · Cited by 77 · see citing works
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An equatorial oscillation in Saturn's middle atmosphere
Fouchet, T., Guerlet, S., Strobel, D. F., Simon-Miller, A. A., Bézard, B., & Flasar, F. M. (2008) · Nature · doi:10.1038/nature06912 · Cited by 115 · see citing works
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General circulation and transport in Saturn’s upper troposphere and stratosphere
Friedson, A. J., & Moses, J. I. (2012) · Icarus · doi:10.1016/j.icarus.2012.02.004 · Cited by 54 · see citing works
Self-citationA hexagon in Saturn's northern stratosphere surrounding the emerging summertime polar vortex
Fletcher, L. N., Orton, G. S., Sinclair, J. A., Guerlet, S., Read, P. L., Antuñano, A., Achterberg, R. K., Flasar, F. M., Irwin, P. G. J., Bjoraker, G. L., et al. (2018) · Nature Communications · doi:10.1038/s41467-018-06017-3 · Cited by 52 · see citing works
Sinclair, J. A., Irwin, P. G. J., Fletcher, L. N., Moses, J. I., Greathouse, T. K., Friedson, A. J., Hesman, B., Hurley, J., & Merlet, C. (2013) · Icarus · doi:10.1016/j.icarus.2013.03.011 · Cited by 49 · see citing works
Self-citationSeasonal evolution of Saturn’s polar temperatures and composition
Fletcher, L. N., Irwin, P. G. J., Sinclair, J. A., Orton, G. S., Giles, R. S., Hurley, J., Gorius, N., Achterberg, R. K., Hesman, B. E., & Bjoraker, G. L. (2015) · Icarus · doi:10.1016/j.icarus.2014.11.022 · Cited by 46 · see citing works
Guerlet, S., Fouchet, T., Bézard, B., Moses, J. I., Fletcher, L. N., Simon-Miller, A. A., & Michael Flasar, F. (2010) · Icarus · doi:10.1016/j.icarus.2010.03.033 · Cited by 45 · see citing works
Self-citationSinclair, J. A., Orton, G. S., Greathouse, T. K., Fletcher, L. N., Moses, J. I., Hue, V., & Irwin, P. G. J. (2018) · Icarus · doi:10.1016/j.icarus.2017.09.016 · Cited by 38 · see citing works
Self-citationGiant Planet Observations with the <i>James Webb Space Telescope</i>
Norwood, J., Moses, J., Fletcher, L. N., Orton, G., Irwin, P. G. J., Atreya, S., Rages, K., Cavalié, T., Sánchez-Lavega, A., Hueso, R., et al. (2016) · Publications of the Astronomical Society of the Pacific · doi:10.1088/1538-3873/128/959/018005 · Cited by 38 · see citing works
Stratospheric benzene and hydrocarbon aerosols detected in Saturn’s auroral regions
Guerlet, S., Fouchet, T., Vinatier, S., Simon, A. A., Dartois, E., & Spiga, A. (2015) · Astronomy & Astrophysics · doi:10.1051/0004-6361/201424745 · Cited by 32 · see citing works
Seasonal changes in Saturn’s stratosphere inferred from Cassini/CIRS limb observations
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Hue, V., Cavalié, T., Dobrijevic, M., Hersant, F., & Greathouse, T. K. (2015) · Icarus · doi:10.1016/j.icarus.2015.04.001 · Cited by 30 · see citing works
“In this section, we first present results from our photochemical model using the spatially uniform thermal field (U) described in 2.3.1 in order to compare with existing models (Moses and Greathouse, 2005).”
BackgroundMethodResultInfluentialSelf-citationHue, V., Greathouse, T. K., Cavalié, T., Dobrijevic, M., & Hersant, F. (2016) · Icarus · doi:10.1016/j.icarus.2015.12.007 · Cited by 21 · see citing works
Self-citation
- Authors
- Moses, J. I., & Greathouse, T. K.
- Affiliations
- Lunar and Planetary Institute (US)
- Venue
- Journal of Geophysical Research: Planets
- Publisher
- American Geophysical Union (AGU)
- Published
- 2005-09
- Volume
- 110
- Issue
- E9
- ISSN
- 0148-0227 (ISSN-L)
- OpenAlex
- W2005523626
- Cited by
- 76
- References
- 1
- Citations by year
- 2025: 1 · 2024: 6 · 2023: 2 · 2022: 2 · 2021: 2 · 2020: 3 · 2019: 2 · 2018: 7 · 2017: 2 · 2016: 3 · 2015: 10 · 2014: 2 · 2013: 4 · 2012: 5
- FWCI
- 2.27
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Journal of Geophysical Research Atmospheres (publishedVersion)
- Topics
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astro and Planetary Science
- Physical Sciences › Earth and Planetary Sciences › Atmospheric Science › Atmospheric Ozone and Climate
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Ionosphere and magnetosphere dynamics
- Keywords
- stratospheric photochemistry, hydrocarbon abundances, acetylene, ethane, vertical diffusion, meridional transport, seasonal variation, latitudinal variation, solar irradiation, photochemical lifetime, IRTF
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