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Seasonal Evolution of Titan's Stratosphere During the Cassini Mission

Teanby, N. A. ; Sylvestre, M. ; Sharkey, J. ; Nixon, C. A. ; Vinatier, S. ; Irwin, P. G. J.

Geophysical research letters, 2019-03, Vol.46 (6), p.3079-3089 [Periódico revisado por pares]

United States: Blackwell Publishing Ltd

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  • Título:
    Seasonal Evolution of Titan's Stratosphere During the Cassini Mission
  • Autor: Teanby, N. A. ; Sylvestre, M. ; Sharkey, J. ; Nixon, C. A. ; Vinatier, S. ; Irwin, P. G. J.
  • Assuntos: Adiabatic ; Adiabatic heating ; Aerodynamics ; Annual variations ; Astrophysics ; Breakup ; Cassini mission ; Chemical evolution ; Composition ; Cooling ; Darkness ; Earth ; Enrichment ; Evolution ; Gas composition ; Gases ; Infrared analysis ; Infrared spectra ; Infrared spectrometers ; Lower atmosphere ; Mapping ; Moon ; Organic chemistry ; Photochemistry ; Physics ; Polar vortex ; Polar winter ; Radiative cooling ; Saturn ; Seasonal variation ; Seasonal variations ; Spacecraft ; Stratosphere ; Subsidence ; Titan ; Trace gases ; Vortices ; Winds ; Winter
  • É parte de: Geophysical research letters, 2019-03, Vol.46 (6), p.3079-3089
  • Notas: ObjectType-Article-1
    SourceType-Scholarly Journals-1
    ObjectType-Feature-2
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  • Descrição: Titan's stratosphere exhibits significant seasonal changes, including breakup and formation of polar vortices. Here we present the first analysis of midinfrared mapping observations from Cassini's Composite InfraRed Spectrometer to cover the entire mission (Ls=293–93°, 2004–2017)—midnorthern winter to northern summer solstice. The north polar winter vortex persisted well after equinox, starting breakup around Ls∼60° and fully dissipating by Ls∼90°. Absence of enriched polar air spreading to lower latitudes suggests large‐scale circulation changes and photochemistry control chemical evolution during vortex breakup. South polar vortex formation commenced soon after equinox and by Ls∼60° was more enriched in trace gases than the northern middle‐winter vortex and had temperatures ∼20 K colder. This suggests that early‐winter and middle‐winter vortices are dominated by different processes—radiative cooling and subsidence‐induced adiabatic heating respectively. By the end of the mission (Ls=93°) south polar conditions were approaching those observed in the north at Ls=293°, implying seasonal symmetry in Titan's vortices. Plain Language Summary The Cassini spacecraft observed Saturn's largest moon, Titan, during its 13‐year tour of the Saturn system. This allowed temperature and gas composition to be measured for almost half a Titan year, which lasts 29.46 Earth years. Spectra measured by Cassini's infrared spectrometer show that Titan's winter poles are much colder and significantly more enriched in trace gas species than more equatorial latitudes. These observations can be explained by the presence of winter polar vortices, where sinking air enriches the composition of the lower atmosphere and isolation by strong vortex winds allows enhanced cooling in the winter darkness. The coldest temperatures and most extreme trace gas concentrations were seen at Titan's southern pole during early winter and vortex formation. Key Points Early‐ and middle‐winter polar vortices have distinct behaviors and different dominant processes Large‐scale dynamics and photochemistry determine polar chemical evolution during vortex breakup The northern winter vortex persisted until late spring, with breakup completed by midsummer
  • Editor: United States: Blackwell Publishing Ltd
  • Idioma: Inglês
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