Seasonal changes in the middle atmosphere of Titan from Cassini/CIRS observations: Temperature and trace species abundance profiles from 2004 to 2017

Mathé, Christophe; Vinatier, Sandrine; Bézard, Bruno; Lebonnois, Sébastien; Gorius, N.; Jennings, Donald E.; Mamoutkine, A. A.; Guandique, E.; d'Ollone, Jan Vatant

doi:10.1016/j.icarus.2019.113547

Cited by 27 publications

(47 citation statements)

References 51 publications

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“…After applying this shift to the lines of sight of the deepest position of the FP4 array, we then determined what shift to apply to the pointing altitudes of the upper pointing position to get a continuity of the entire radiance vertical profile (including both pointing positions). A similar method was also used by Mathé et al (2020) for all CIRS limb spectra acquired at a 0.5-cm −1 spectral resolution. The applied shifts are given in Table B.1.…”

Section: Retrieval Of the Temperature And Photochemical Compound Miximentioning

confidence: 99%

“…As HC 3 N, CO 2 , and C 6 H 6 emission bands are mixed, and as the CO 2 VMR does not vary with latitude or season (Vinatier et al 2015;Mathé et al 2020), we fixed the CO 2 VMR profile to the one derived by Vinatier et al (2015) at 0 • N in May 2012. The HC 3 N and C 6 H 6 mixing ratio profiles were retrieved from the fit of the 660-678 cm −1 spectral range.…”

Section: Retrieval Of the Temperature And Photochemical Compound Miximentioning

confidence: 99%

“…The temperature profiles we derived can be compared with those of Mathé et al (2020) inferred from CIRS limb spectra acquired at 0.5-cm −1 spectral resolution at comparable latitudes and time. Their dataset probed the same pressure region as ours.…”

Section: Thermal Fieldmentioning

confidence: 99%

“…One of the most striking events of the southern fall was the unexpected 30 K cooling of the polar stratopause and mesosphere between June 2011 and February 2012 (L s = 22.7 • −30.6 • ) (Teanby et al 2017;Vinatier et al 2015) at least partly explained by the increased efficiency of radiative cooling by the strongly enhanced photochemical species and the decreasing solar flux, while the subsidence was strengthening the adiabatic heating (Teanby et al 2017). The southern polar enrichment continued to strengthen after this date, reaching its maximum in March 2015 (L s = 65.8 • ;Mathé et al 2020), while the polar stratospheric temperature continually decreased before increasing again around September 2015 (L s = 72 • ) (Teanby et al 2017). The southern molecular polar enrichment combined with the low stratospheric temperatures were at the origin of the development of a large stratospheric polar cloud first observed in May 2012 by the Cassini Imager SubSystem (ISS; West et al 2016).…”

Section: Introductionmentioning

confidence: 98%

“…The Cassini mission arrived at the Saturn system on July 1, 2004 (L s = 293 • ), during the middle of Saturn's northern winter and ended on September 15, 2017 (L s = 93 • ), a few months after the northern summer solstice. Titan Global Climate Models (GCMs) predict that during northern winter the global dynamics of Titan's middle atmosphere (from the deep stratosphere to the mesosphere) consists A&A 641, A116 (2020) produced at higher altitude levels towards the deep stratosphere where some molecules such as HC 3 N or C 4 H 2 were observed to be enhanced by several orders of magnitude compared to their values outside the winter polar vortex (Coustenis et al 2007;Mathé et al 2020;Teanby et al 2007Teanby et al , 2008Vinatier et al 2007Vinatier et al , 2010a. Around the northern spring equinox, which occurred on August 11, 2009 (L s = 0 • ), GCM predict changes of this dynamical pattern with a two-year transition period involving a two-cell circulation regime with air upwelling at low latitudes and subsidence at both poles.…”

Section: Introductionmentioning

confidence: 99%

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Temperature and chemical species distributions in the middle atmosphere observed during Titan’s late northern spring to early summer

Vinatier

Mathé

Bézard

et al. 2020

A&A

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We present a study of the seasonal evolution of Titan’s thermal field and distributions of haze, C2H2, C2H4, C2H6, CH3C2H, C3H8, C4H2, C6H6, HCN, and HC3N from March 2015 (Ls = 66°) to September 2017 (Ls = 93°) (i.e., from the last third of northern spring to early summer). We analyzed thermal emission of Titan’s atmosphere acquired by the Cassini Composite Infrared Spectrometer with limb and nadir geometry to retrieve the stratospheric and mesospheric temperature and mixing ratios pole-to-pole meridional cross sections from 5 mbar to 50 μbar (120–650 km). The southern stratopause varied in a complex way and showed a global temperature increase from 2015 to 2017 at high-southern latitudes. Stratospheric southern polar temperatures, which were observed to be as low as 120 K in early 2015 due to the polar night, showed a 30 K increase (at 0.5 mbar) from March 2015 to May 2017 due to adiabatic heating in the subsiding branch of the global overturning circulation. All photochemical compounds were enriched at the south pole by this subsidence. Polar cross sections of these enhanced species, which are good tracers of the global dynamics, highlighted changes in the structure of the southern polar vortex. These high enhancements combined with the unusually low temperatures (<120 K) of the deep stratosphere resulted in condensation at the south pole between 0.1 and 0.03 mbar (240–280 km) of HCN, HC3N, C6H6 and possibly C4H2 in March 2015 (Ls = 66°). These molecules were observed to condense deeper with increasing distance from the south pole. At high-northern latitudes, stratospheric enrichments remaining from the winter were observed below 300 km between 2015 and May 2017 (Ls = 90°) for all chemical compounds and up to September 2017 (Ls = 93°) for C2H2, C2H4, CH3C2H, C3H8, and C4H2. In September 2017, these local enhancements were less pronounced than earlier for C2H2, C4H2, CH3C2H, HC3N, and HCN, and were no longer observed for C2H6 and C6 H6, which suggests a change in the northern polar dynamics near the summer solstice. These enhancements observed during the entire spring may be due to confinement of this enriched air by a small remaining winter circulation cell that persisted in the low stratosphere up to the northern summer solstice, according to predictions of the Institut Pierre Simon Laplace Titan Global Climate Model (IPSL Titan GCM). In the mesosphere we derived a depleted layer in C2H2, HCN, and C2H6 from the north pole to mid-southern latitudes, while C4H2, C3H4, C2H4, and HC3N seem to have been enriched in the same region. In the deep stratosphere, all molecules except C2H4 were depleted due to their condensation sink located deeper than 5 mbar outside the southern polar vortex. HCN, C4H2, and CH3C2H volume mixing ratio cross section contours showed steep slopes near the mid-latitudes or close to the equator, which can be explained by upwelling air in this region. Upwelling is also supported by the cross section of the C2H4 (the only molecule not condensing among those studied here) volume mixing ratio observed in the northern hemisphere. We derived the zonal wind velocity up to mesospheric levels from the retrieved thermal field. We show that zonal winds were faster and more confined around the south pole in 2015 (Ls = 67−72°) than later. In 2016, the polar zonal wind speed decreased while the fastest winds had migrated toward low-southern latitudes.

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Section: Retrieval Of the Temperature And Photochemical Compound Miximentioning

confidence: 99%

Section: Retrieval Of the Temperature And Photochemical Compound Miximentioning

confidence: 99%

Section: Thermal Fieldmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Temperature and chemical species distributions in the middle atmosphere observed during Titan’s late northern spring to early summer

Vinatier

Mathé

Bézard

et al. 2020

A&A

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Winter Weakening of Titan's Stratospheric Polar Vortices 1

Shultis

Waugh

Toigo

et al. 2022

Preprint

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Science goals and new mission concepts for future exploration of Titan’s atmosphere, geology and habitability: titan POlar scout/orbitEr and in situ lake lander and DrONe explorer (POSEIDON)

et al. 2022

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In response to ESA’s “Voyage 2050” announcement of opportunity, we propose an ambitious L-class mission to explore one of the most exciting bodies in the Solar System, Saturn’s largest moon Titan. Titan, a “world with two oceans”, is an organic-rich body with interior-surface-atmosphere interactions that are comparable in complexity to the Earth. Titan is also one of the few places in the Solar System with habitability potential. Titan’s remarkable nature was only partly revealed by the Cassini-Huygens mission and still holds mysteries requiring a complete exploration using a variety of vehicles and instruments. The proposed mission concept POSEIDON (Titan POlar Scout/orbitEr and In situ lake lander DrONe explorer) would perform joint orbital and in situ investigations of Titan. It is designed to build on and exceed the scope and scientific/technological accomplishments of Cassini-Huygens, exploring Titan in ways that were not previously possible, in particular through full close-up and in situ coverage over long periods of time. In the proposed mission architecture, POSEIDON consists of two major elements: a spacecraft with a large set of instruments that would orbit Titan, preferably in a low-eccentricity polar orbit, and a suite of in situ investigation components, i.e. a lake lander, a “heavy” drone (possibly amphibious) and/or a fleet of mini-drones, dedicated to the exploration of the polar regions. The ideal arrival time at Titan would be slightly before the next northern Spring equinox (2039), as equinoxes are the most active periods to monitor still largely unknown atmospheric and surface seasonal changes. The exploration of Titan’s northern latitudes with an orbiter and in situ element(s) would be highly complementary in terms of timing (with possible mission timing overlap), locations, and science goals with the upcoming NASA New Frontiers Dragonfly mission that will provide in situ exploration of Titan’s equatorial regions, in the mid-2030s.

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Seasonal changes in the middle atmosphere of Titan from Cassini/CIRS observations: Temperature and trace species abundance profiles from 2004 to 2017

Cited by 27 publications

References 51 publications

Temperature and chemical species distributions in the middle atmosphere observed during Titan’s late northern spring to early summer

Temperature and chemical species distributions in the middle atmosphere observed during Titan’s late northern spring to early summer

Winter Weakening of Titan's Stratospheric Polar Vortices 1

Science goals and new mission concepts for future exploration of Titan’s atmosphere, geology and habitability: titan POlar scout/orbitEr and in situ lake lander and DrONe explorer (POSEIDON)

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