The evolution of Titan's detached haze layer near equinox in 2009

West, Robert A.; Balloch, J.; Dumont, Philip; Lavvas, P.; Lorenz, Ralph D.; Rannou, P.; Ray, T. L.; Turtle, E. P.

doi:10.1029/2011gl046843

Cited by 53 publications

(74 citation statements)

References 21 publications

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“…Titan's atmosphere is photochemically active even at lower altitudes and leads to the formation of complex tholin-like potential prebiotic molecules due to the penetrating longer wavelength photons. This is consistent with observations of Titan's haze stretching between B500 km and B50 km above the surface 9 , containing several regions of haze (0, A, B and C) as recently characterized by the Cassini CIRS instrument 34,35 .…”

supporting

confidence: 92%

Photochemical activity of Titan’s low-altitude condensed haze

et al. 2013

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Titan, the largest moon of Saturn and similar to Earth in many aspects, has unique orangeyellow colour that comes from its atmospheric haze, whose formation and dynamics are far from well understood. Present models assume that Titan's tholin-like haze formation occurs high in atmosphere through gas-phase chemical reactions initiated by high-energy solar radiation. Here we address an important question: Is the lower atmosphere of Titan photochemically active or inert? We demonstrate that indeed tholin-like haze formation could occur on condensed aerosols throughout the atmospheric column of Titan. Detected in Titan's atmosphere, dicyanoacetylene (C 4 N 2 ) is used in our laboratory simulations as a model system for other larger unsaturated condensing compounds. We show that C 4 N 2 ices undergo condensed-phase photopolymerization (tholin formation) at wavelengths as long as 355 nm pertinent to solar radiation reaching a large portion of Titan's atmosphere, almost close to the surface.

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confidence: 92%

Photochemical activity of Titan’s low-altitude condensed haze

et al. 2013

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“…Indeed, short-term variations observed during the Cassini mission can arise from changes in the circulation around the time of the equinox. The collapse of the detached aerosol layer (West et al 2011) suggests that the dynamics during this period go through a rapid transition which should also affect the gas distribution. The rapid decrease after mid-2009, for which the most straightforward explanation is that the vortex has shrunk somewhat, would be consistent with the weakening thermal gradient we find here and that of the winds also reported by Achterberg et al (2008Achterberg et al ( , 2011 and Teanby et al (2009b).…”

Section: Discussion Of the Results And Possible Interpretationsmentioning

confidence: 99%

THERMAL AND CHEMICAL STRUCTURE VARIATIONS IN TITAN'S STRATOSPHERE DURING THECASSINIMISSION

Bampasidis

Coustenis

Achterberg

et al. 2012

ApJ

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We have developed a line-by-line Atmospheric Radiative Transfer for Titan code that includes the most recent laboratory spectroscopic data and haze descriptions relative to Titan's stratosphere. We use this code to model Cassini Composite Infrared Spectrometer data taken during the numerous Titan flybys from 2006 to 2012 at surface-intercepting geometry in the 600-1500 cm −1 range for latitudes from 50 • S to 50 • N. We report variations in temperature and chemical composition in the stratosphere during the Cassini mission, before and after the Northern Spring Equinox (NSE). We find indication for a weakening of the temperature gradient with warming of the stratosphere and cooling of the lower mesosphere. In addition, we infer precise concentrations for the trace gases and their main isotopologues and find that the chemical composition in Titan's stratosphere varies significantly with latitude during the 6 years investigated here, with increased mixing ratios toward the northern latitudes. In particular, we monitor and quantify the amplitude of a maximum enhancement of several gases observed at northern latitudes up to 50 • N around mid-2009, at the time of the NSE. We find that this rise is followed by a rapid decrease in chemical inventory in 2010 probably due to a weakening north polar vortex with reduced lateral mixing across the vortex boundary.

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“…These investigations have shown that a large-scale reversal occurred in the single pole-to-pole circulation affecting the distribution of the atmospheric structure after the northern equinox in mid-2009, with the gases in the summer hemisphere showing upwelling while in the winter pole a corresponding subsidence was found (Achterberg et al 2008(Achterberg et al , 2011Bampasidis et al 2012;Teanby et al 2012). Whereas until 2011 a significant build-up of trace gases, haze, and condensates was still observed over the north pole (West et al 2011(West et al , 2016Jennings et al 2012aJennings et al , 2012bCoustenis et al 2013;Vinatier et al 2015), toward the end of that period, the vortex and hotspot reported in Jennings et al (2015) and Achterberg et al (2008) had practically disappeared. In its place, similar features started to appear near the south pole, which have evolved to what we see today.In the absence of sunlight, gases that subsidize have accumulated since 2012 and become enhanced (e.g., Coustenis et al 2016 and references within;Teanby et al 2017), and a subset of those have been suggested to be causing the haze decrease found in the north and its subsequent increase in the south (Jennings et al 2012b(Jennings et al , 2015.…”

Section: Introductionmentioning

confidence: 96%

Seasonal Evolution of Titan's Stratosphere Near the Poles

Coustenis

Jennings

Achterberg

et al. 2018

ApJL

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In this Letter, we report the monitoring of seasonal evolution near Titan's poles. We find Titan's south pole to exhibit since 2010 a strong temperature decrease and a dramatic enhancement of several trace species such as complex hydrocarbons and nitriles (HC 3 N and C 6 H 6 in particular) previously only observed at high northern latitudes. This results from the seasonal change on Titan going from winter (2002) to summer (2017) in the north and, at the same time, the onset of winter in the south pole. During this transition period atmospheric components with longer chemical lifetimes linger in the north, undergoing slow photochemical destruction, while those with shorter lifetimes decrease and reappear in the south. An opposite effect was expected in the north, but not observed with certainty until now. We present here an analysis of high-resolution nadir spectra acquired by Cassini/Cassini Composite Infrared Spectrometer in the past years and describe the temperature and composition variations near Titan's poles. From 2013 until 2016, the northern polar region has shown a temperature increase of 10 K, while the south has shown a more significant decrease (up to 25 K) in a similar period of time. While the south polar region has been continuously enhanced since about 2012, the chemical content in the north is finally showing a clear depletion for most molecules only since 2015. This is indicative of a non-symmetrical response to the seasons in Titan's stratosphere that can set constraints on photochemical and GCM models.

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The evolution of Titan's detached haze layer near equinox in 2009

Cited by 53 publications

References 21 publications

Photochemical activity of Titan’s low-altitude condensed haze

Photochemical activity of Titan’s low-altitude condensed haze

THERMAL AND CHEMICAL STRUCTURE VARIATIONS IN TITAN'S STRATOSPHERE DURING THECASSINIMISSION

Seasonal Evolution of Titan's Stratosphere Near the Poles

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