pubtitan0.bib
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@comment{{Command line: bib2bib --quiet -c abstract:"Titan" -c $type="ARTICLE" -oc pubtitan0.txt -ob pubtitan0.bib lebonnois.link.bib}}
@article{2022A&A...658A.108C,
author = {{Charnay}, B. and {Tobie}, G. and {Lebonnois}, S. and {Lorenz}, R.~D.},
title = {{Gravitational atmospheric tides as a probe of Titan's interior: Application to Dragonfly}},
journal = {\aap},
keywords = {planets and satellites: individual: Titan, planets and satellites: atmospheres, planets and satellites: interiors, Astrophysics - Earth and Planetary Astrophysics},
year = 2022,
month = feb,
volume = {658},
eid = {A108},
pages = {A108},
abstract = {{Context. Saturn's massive gravity is expected to causes a tide in
Titan's atmosphere, producing a surface pressure variation
through the orbit of Titan and tidal winds in the troposphere.
The future Dragonfly mission could analyse this exotic
meteorological phenomenon. \textbackslash Aims: We aim to
analyse the effect of Saturn's tides on Titan's atmosphere and
interior to determine how pressure measurements by Dragonfly
could constrain Titan's interior. \textbackslash Methods: We
model atmospheric tides with analytical calculations and with a
3D global climate model (the IPSL-Titan GCM), including the
tidal response of the interior. \textbackslash Results: We
predict that the Love numbers of Titan's interior should verify
1 + ℜ(k$_{2}$ {\ensuremath{-}} h$_{2}$)
\raisebox{-0.5ex}\textasciitilde 0.02-0.1 and ℑ(k$_{2}$
{\ensuremath{-}} h$_{2}$) < 0.04. The deformation of Titan's
interior should therefore strongly weaken gravitational
atmospheric tides, yielding a residual surface pressure
amplitude of only \raisebox{-0.5ex}\textasciitilde5 Pa, with a
phase shift of 5-20 h. Tidal winds are very weak, of the order
of 3 {\texttimes} 10$^{{\ensuremath{-}}4}$ m
s$^{{\ensuremath{-}}1}$ in the lower troposphere. Finally,
constraints from Dragonfly data may permit the real and the
imaginary parts of k$_{2}$ {\ensuremath{-}} h$_{2}$ to be
estimated with a precision of {\ensuremath{\pm}}0.01-0.03.
\textbackslash Conclusions: Measurements of pressure variations
by Dragonfly over the whole mission could give valuable
constraints on the thickness of Titan's ice shell, and, via
geophysical models, its heat flux and the density of its
internal ocean.}},
doi = {10.1051/0004-6361/202141898},
archiveprefix = {arXiv},
eprint = {2111.02199},
primaryclass = {astro-ph.EP},
localpdf = {REF/2022A&A...658A.108C.pdf},
adsurl = {https://ui.adsabs.harvard.edu/abs/2022A&A...658A.108C},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2022ExA...tmp....2R,
author = {{Rodriguez}, S. and {Vinatier}, S. and {Cordier}, D. and {Tobie}, G. and {Achterberg}, R. K. and {Anderson}, C. M. and {Badman}, S. V. and {Barnes}, J. W. and {Barth}, E. L. and {B{\'e}zard}, B. and {Carrasco}, N. and {Charnay}, B. and {Clark}, R. N. and {Coll}, P. and {Cornet}, T. and {Coustenis}, A. and {Couturier-Tamburelli}, I. and {Dobrijevic}, M. and {Flasar}, F. M. and {de Kok}, R. and {Freissinet}, C. and {Galand}, M. and {Gautier}, T. and {Geppert}, W. D. and {Griffith}, C. A. and {Gudipati}, M. S. and {Hadid}, L. Z. and {Hayes}, A. G. and {Hendrix}, A. R. and {Jaumann}, R. and {Jennings}, D. E. and {Jolly}, A. and {Kalousova}, K. and {Koskinen}, T. T. and {Lavvas}, P. and {Lebonnois}, S. and {Lebreton}, J.-P. and {Le Gall}, A. and {Lellouch}, E. and {Le Mou{\'e}lic}, S. and {Lopes}, R. M.~C. and {Lora}, J. M. and {Lorenz}, R. D. and {Lucas}, A. and {MacKenzie}, S. and {Malaska}, M. J. and {Mandt}, K. and {Mastrogiuseppe}, M. and {Newman}, C. E. and {Nixon}, C. A. and {Radebaugh}, J. and {Rafkin}, S. C. and {Rannou}, P. and {Sciamma-O'Brien}, E. M. and {Soderblom}, J. M. and {Solomonidou}, A. and {Sotin}, C. and {Stephan}, K. and {Strobel}, D. and {Szopa}, C. and {Teanby}, N. A. and {Turtle}, E. P. and {Vuitton}, V. and {West}, R. A.},
title = {{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)}},
journal = {Experimental Astronomy},
keywords = {Titan, Atmosphere, Geology, Habitability, Orbiter, Lake lander, Drones, Astrophysics - Earth and Planetary Astrophysics, Astrophysics - Instrumentation and Methods for Astrophysics},
year = 2022,
month = jan,
abstract = {{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.}},
doi = {10.1007/s10686-021-09815-8},
archiveprefix = {arXiv},
eprint = {2110.10466},
primaryclass = {astro-ph.EP},
localpdf = {REF/2022ExA...tmp....2R.pdf},
adsurl = {https://ui.adsabs.harvard.edu/abs/2022ExA...tmp....2R},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2021ApJ...922..239R,
author = {{Rannou}, P. and {Coutelier}, M. and {Rivi{\`e}re}, E. and {Lebonnois}, S. and {Rey}, M. and {Maltagliati}, L.},
title = {{Convection behind the Humidification of Titan's Stratosphere}},
journal = {\apj},
keywords = {1244, 2184, 2120},
year = 2021,
month = dec,
volume = {922},
number = {2},
eid = {239},
pages = {239},
abstract = {{On Titan, methane is responsible for the complex prebiotic chemistry,
the global haze, most of the cloud cover, and the rainfall that
models the landscape. Its sources are located in liquid
reservoirs at and below the surface, and its sink is the
photodissociation at high altitude. Titan's present and past
climates strongly depend on the connection between the surface
sources and the atmosphere upper layers. Despite its importance,
very little information is available on this topic. In this
work, we reanalyze two solar occultations made by Cassini before
the northern spring equinox. We find a layer rich in methane at
165 km and at 70{\textdegree}S (mixing ratio 1.62\%
{\ensuremath{\pm}} 0.1\%) and a dryer background stratosphere
(1.1\%-1.2\%). In the absence of local production, this reveals
an intrusion of methane transported into the stratosphere by
convective circulation. On the other hand, methane transport
through the tropopause at a global scale appears quite
inhibited. Leaking through the tropopause is an important
bottleneck of Titan's methane cycle at all timescales. As such,
it affects the long-term evolution of Titan's atmosphere and the
exchange fluxes with the surface and subsurface reservoirs in a
complex way. Global climate models accounting for cloud physics,
thermodynamical feedbacks, and convection are needed to
understand the methane cycle, and specifically the
humidification of the stratosphere, at the present time, and its
evolution under changing conditions at a geological timescale.}},
doi = {10.3847/1538-4357/ac2904},
localpdf = {REF/2021ApJ...922..239R.pdf},
adsurl = {https://ui.adsabs.harvard.edu/abs/2021ApJ...922..239R},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2020A&A...641A.116V,
author = {{Vinatier}, S. and {Math{\'e}}, C. and {B{\'e}zard}, B. and {Vatant d'Ollone}, J. and {Lebonnois}, S. and {Dauphin}, C. and {Flasar}, F.~M. and {Achterberg}, R.~K. and {Seignovert}, B. and {Sylvestre}, M. and {Teanby}, N.~A. and {Gorius}, N. and {Mamoutkine}, A. and {Guandique}, E. and {Jennings}, D.~E.},
title = {{Temperature and chemical species distributions in the middle atmosphere observed during Titan's late northern spring to early summer}},
journal = {\aap},
keywords = {planets and satellites: individual: Titan, planets and satellites: atmospheres, planets and satellites: composition, methods: data analysis, radiative transfer, infrared: planetary systems},
year = 2020,
month = sep,
volume = {641},
eid = {A116},
pages = {A116},
abstract = {{We present a study of the seasonal evolution of Titan's thermal field
and distributions of haze, C$_{2}$H$_{2}$, C$_{2}$H$_{4}$,
C$_{2}$H$_{6}$, CH$_{3}$C$_{2}$H, C$_{3}$H$_{8}$,
C$_{4}$H$_{2}$, C$_{6}$H$_{6}$, HCN, and HC$_{3}$N from March
2015 (L$_{s}$ = 66{\textdegree}) to September 2017 (L$_{s}$ =
93{\textdegree}) (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
{\ensuremath{\mu}}bar (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, HC$_{3}$N, C$_{6}$H$_{6}$ and possibly
C$_{4}$H$_{2}$ in March 2015 (L$_{s}$ = 66{\textdegree}). 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 (L$_{s}$ =
90{\textdegree}) for all chemical compounds and up to September
2017 (L$_{s}$ = 93{\textdegree}) for C$_{2}$H$_{2}$,
C$_{2}$H$_{4}$, CH$_{3}$C$_{2}$H, C$_{3}$H$_{8}$, and
C$_{4}$H$_{2}$. In September 2017, these local enhancements were
less pronounced than earlier for C$_{2}$H$_{2}$, C$_{4}$H$_{2}$,
CH$_{3}$C$_{2}$H, HC$_{3}$N, and HCN, and were no longer
observed for C$_{2}$H$_{6}$ and C$_{6}$ H$_{6}$, 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 C$_{2}$H$_{2}$, HCN, and C$_{2}$H$_{6}$ from
the north pole to mid-southern latitudes, while C$_{4}$H$_{2}$,
C$_{3}$H$_{4}$, C$_{2}$H$_{4}$, and HC$_{3}$N seem to have been
enriched in the same region. In the deep stratosphere, all
molecules except C$_{2}$H$_{4}$ were depleted due to their
condensation sink located deeper than 5 mbar outside the
southern polar vortex. HCN, C$_{4}$H$_{2}$, and CH$_{3}$C$_{2}$H
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 C$_{2}$H$_{4}$ (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 (L$_{s}$ =
67-72{\textdegree}) than later. In 2016, the polar zonal wind
speed decreased while the fastest winds had migrated toward low-
southern latitudes. \textbackslash\textbackslashThe data are
only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-
bin/cat/J/A+A/641/A116}},
doi = {10.1051/0004-6361/202038411},
localpdf = {REF/2020A&A...641A.116V.pdf},
adsurl = {https://ui.adsabs.harvard.edu/abs/2020A&A...641A.116V},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2020SSRv..216...87I,
author = {{Imamura}, T. and {Mitchell}, J. and {Lebonnois}, S. and
{Kaspi}, Y. and {Showman}, A. P. and {Korablev}, O.},
title = {{Superrotation in Planetary Atmospheres}},
journal = {\ssr},
keywords = {Superrotation, Planetary atmosphere, Venus, Titan, Gas giants, Exoplanets},
year = 2020,
month = jul,
volume = {216},
number = {5},
eid = {87},
pages = {87},
abstract = {{Superrotation is a dynamical regime where the atmosphere circulates around the planet in the direction of planetary rotation with excess angular momentum in the equatorial region. Superrotation is known to exist in the atmospheres of Venus, Titan, Jupiter, and Saturn in the solar system. Some of the exoplanets also exhibit superrotation. Our understanding of superrotation in a framework of circulation regimes of the atmospheres of terrestrial planets is in progress thanks to the development of numerical models; a global instability involving planetary-scale waves seems to play a key role, and the dynamical state depends on the Rossby number, a measure of the relative importance of the inertial and Coriolis forces, and the thermal inertia of the atmosphere. Recent general circulation models of Venus's and Titan's atmospheres demonstrated the importance of horizontal waves in the angular momentum transport in these atmospheres and also an additional contribution of thermal tides in Venus's atmosphere. The atmospheres of Jupiter and Saturn also exhibit strong superrotation. Recent gravity data suggests that these superrotational flows extend deep into the planet, yet currently no single mechanism has been identified as driving this superrotation. Moreover, atmospheric circulation models of tidally locked, strongly irradiated exoplanets have long predicted the existence of equatorial superrotation in their atmospheres, which has been attributed to the result of the strong day-night thermal forcing. As predicted, recent Doppler observations and infrared phase curves of hot Jupiters appear to confirm the presence of superrotation on these objects.
}},
localpdf = {REF/2020SSRv..216...87I.pdf},
doi = {10.1007/s11214-020-00703-9},
adsurl = {https://ui.adsabs.harvard.edu/abs/2020SSRv..216...87I},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2020Icar..34413547M,
author = {{Math{\'e}}, C. and {Vinatier}, S. and {B{\'e}zard}, B. and {Lebonnois}, S. and
{Gorius}, N. and {Jennings}, D. E. and {Mamoutkine}, A. and {Guandique}, E. and {Vatant d'Ollone}, J.},
title = {{Seasonal changes in the middle atmosphere of Titan from Cassini/CIRS observations: Temperature and trace species abundance profiles from 2004 to 2017}},
journal = {\icarus},
keywords = {Titan, atmosphere, Infrared observations, Atmospheres, structure, composition, Astrophysics - Earth and Planetary Astrophysics},
year = 2020,
month = jul,
volume = {344},
eid = {113547},
pages = {113547},
abstract = {{The Cassini/Composite InfraRed Spectrometer (CIRS) instrument has been observing the middle atmosphere of Titan over almost half a Saturnian year. We used the CIRS dataset processed through the up-to-date calibration pipeline to characterize seasonal changes of temperature and abundance profiles in the middle atmosphere of Titan, from mid-northern winter to early northern summer all around the satellite. We used limb spectra from 590 to 1500 cm-1 at 0.5-cm-1 spectral resolution, which allows us to probe different altitudes. We averaged the limb spectra recorded during each flyby on a fixed altitude grid to increase the signal-to-noise ratio. These thermal infrared data were analyzed by means of a radiative transfer code coupled with an inversion algorithm, in order to retrieve vertical temperature and abundance profiles. These profiles cover an altitude range of approximately 100 to 600 km, at 10- or 40-km vertical resolution (depending on the observation). Strong changes in temperature and composition occur in both polar regions where a vortex is in place during the winter. At this season, we observe a global enrichment in photochemical compounds in the mesosphere and stratosphere and a hot stratopause located around 0.01 mbar, both linked to downwelling in a pole-to-pole circulation cell. After the northern spring equinox, between December 2009 and April 2010, a stronger enhancement of photochemical compounds occurred at the north pole above the 0.01-mbar region, likely due to combined photochemical and dynamical effects. During the southern autumn in 2015, above the South pole, we also observed a strong enrichment in photochemical compounds that contributed to the cooling of the stratosphere above 0.2 mbar (∼300 km). Close to the northern spring equinox, in December 2009, the thermal profile at 74°N exhibits an oscillation that we interpret in terms of an inertia-gravity wave.
}},
localpdf = {REF/2020Icar..34413547M.pdf},
doi = {10.1016/j.icarus.2019.113547},
archiveprefix = {arXiv},
eprint = {1910.12677},
primaryclass = {astro-ph.EP},
adsurl = {https://ui.adsabs.harvard.edu/abs/2020Icar..34413547M},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2020Icar..34413188S,
author = {{Sylvestre}, M. and {Teanby}, N.~A. and {Vatant d'Ollone}, J. and
{Vinatier}, S. and {B{\'e}zard}, B. and {Lebonnois}, S. and
{Irwin}, P.~G.~J.},
title = {{Seasonal evolution of temperatures in Titan's lower stratosphere}},
journal = {\icarus},
keywords = {Astrophysics - Earth and Planetary Astrophysics},
year = 2020,
month = jul,
volume = {344},
eid = {113188},
pages = {113188},
abstract = {{The Cassini mission offered us the opportunity to monitor the seasonal evolution of Titan's atmosphere from 2004 to 2017, i.e. half a Titan year. The lower part of the stratosphere (pressures greater than 10 mbar) is a region of particular interest as there are few available temperature measurements, and because its thermal response to the seasonal and meridional insolation variations undergone by Titan remain poorly known. In this study, we measure temperatures in Titan's lower stratosphere between 6 mbar and 25 mbar using Cassini/CIRS spectra covering the whole duration of the mission (from 2004 to 2017) and the whole latitude range. We can thus characterize the meridional distribution of temperatures in Titan's lower stratosphere, and how it evolves from northern winter (2004) to summer solstice (2017). Our measurements show that Titan's lower stratosphere undergoes significant seasonal changes, especially at the South pole, where temperature decreases by 19 K at 15 mbar in 4 years.
}},
localpdf = {REF/2020Icar..34413188S.pdf},
doi = {10.1016/j.icarus.2019.02.003},
archiveprefix = {arXiv},
eprint = {1902.01841},
primaryclass = {astro-ph.EP},
adsurl = {https://ui.adsabs.harvard.edu/abs/2020Icar..34413188S},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2020Sci...368..363L,
author = {{Lebonnois}, Sebastien},
title = {{Super-rotating the venusian atmosphere}},
journal = {Science},
keywords = {PLANET SCI},
year = 2020,
month = apr,
volume = {368},
number = {6489},
pages = {363-364},
abstract = {{Among the intriguing mysteries that remain for planetary atmospheres, the phenomenon of super-rotation is still a teasing problem. An atmosphere in super-rotation rotates globally faster than the solid body of the planet. In our solar system, super-rotation is observed on Venus and the largest moon of Saturn, Titan (1). The challenge is to explain how angular momentum can accumulate in the atmosphere and what controls the atmospheric angular momentum budget. On page 405 of this issue, Horinouchi et al. (2) address this by analyzing observation data from the onboard cameras of the Venus-orbiting Akatsuki spacecraft.
}},
localpdf = {http://science.sciencemag.org/cgi/rapidpdf/368/6489/363?ijkey=tjVIn/vqqICPI&keytype=ref&siteid=sci},
doi = {10.1126/science.abb2424},
adsurl = {https://ui.adsabs.harvard.edu/abs/2020Sci...368..363L},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2019Icar..333..113L,
author = {{Lora}, J.~M. and {Tokano}, T. and {Vatant d'Ollone}, J. and
{Lebonnois}, S. and {Lorenz}, R.~D.},
title = {{A model intercomparison of Titan's climate and low-latitude environment}},
journal = {\icarus},
keywords = {Titan, Climate, Atmospheres, Meteorology},
year = 2019,
volume = 333,
pages = {113-126},
abstract = {{Cassini-Huygens provided a wealth of data with which to constrain
numerical models of Titan. Such models have been employed over the last
decade to investigate various aspects of Titan's atmosphere and climate,
and several three-dimensional general circulation models (GCMs) now
exist that simulate Titan with a high degree of fidelity. However,
substantial uncertainties persist, and at the same time no dedicated
intercomparisons have assessed the degree to which these models agree
with each other or the observations. To address this gap, and motivated
by the proposed Dragonfly Titan lander mission, we directly compare
three Titan GCMs to each other and to in situ observations, and also
provide multi-model expectations for the low-latitude environment during
the early northern winter season. Globally, the models qualitatively
agree in their representation of the atmospheric structure and
circulation, though one model severely underestimates meridional
temperature gradients and zonal winds. We find that, at low latitudes,
simulated and observed atmospheric temperatures closely agree in all
cases, while the measured winds above the boundary layer are only
quantitatively matched by one model. Nevertheless, the models simulate
similar near-surface winds, and all indicate these are weak. Likewise,
temperatures and methane content at low latitudes are similar between
models, with some differences that are largely attributable to modeling
assumptions. All models predict environments that closely resemble that
encountered by the Huygens probe, including little or no precipitation
at low latitudes during northern winter. The most significant
differences concern the methane cycle, though the models are least
comparable in this area and substantial uncertainties remain. We suggest
that, while the overall low-latitude environment on Titan at this season
is now fairly well constrained, future in situ measurements and
monitoring will transform our understanding of regional and temporal
variability, atmosphere-surface coupling, Titan's methane cycle, and
modeling thereof.
}},
doi = {10.1016/j.icarus.2019.05.031},
adsurl = {https://ui.adsabs.harvard.edu/abs/2019Icar..333..113L},
localpdf = {REF/2019Icar..333..113L.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2018AREPS..46..175R,
author = {{Read}, P.~L. and {Lebonnois}, S.},
title = {{Superrotation on Venus, on Titan, and Elsewhere}},
journal = {Annual Review of Earth and Planetary Sciences},
year = 2018,
volume = 46,
pages = {175-202},
abstract = {{The superrotation of the atmospheres of Venus and Titan has puzzled
dynamicists for many years and seems to put these planets in a very
different dynamical regime from most other planets. In this review, we
consider how to define superrotation objectively and explore the
constraints that determine its occurrence. Atmospheric superrotation
also occurs elsewhere in the Solar System and beyond, and we compare
Venus and Titan with Earth and other planets for which wind estimates
are available. The extreme superrotation on Venus and Titan poses some
difficult challenges for numerical models of atmospheric circulation,
much more difficult than for more rapidly rotating planets such as Earth
or Mars. We consider mechanisms for generating and maintaining a
superrotating state, all of which involve a global meridional
overturning circulation. The role of nonaxisymmetric eddies is crucial,
however, but the detailed mechanisms may differ between Venus, Titan,
and other planets.
}},
doi = {10.1146/annurev-earth-082517-010137},
adsurl = {https://ui.adsabs.harvard.edu/abs/2018AREPS..46..175R},
localpdf = {REF/2018AREPS..46..175R.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2018A&A...609A..64S,
author = {{Sylvestre}, M. and {Teanby}, N.~A. and {Vinatier}, S. and {Lebonnois}, S. and
{Irwin}, P.~G.~J.},
title = {{Seasonal evolution of C$_{2}$N$_{2}$, C$_{3}$H$_{4}$, and C$_{4}$H$_{2}$ abundances in Titan's lower stratosphere}},
journal = {\aap},
archiveprefix = {arXiv},
eprint = {1709.09979},
primaryclass = {astro-ph.EP},
keywords = {planets and satellites: atmospheres, methods: data analysis},
year = 2018,
volume = 609,
eid = {A64},
pages = {A64},
abstract = {{
Aims: We study the seasonal evolution of Titan's lower
stratosphere (around 15 mbar) in order to better understand the
atmospheric dynamics and chemistry in this part of the atmosphere.
Methods: We analysed Cassini/CIRS far-IR observations from 2006 to
2016 in order to measure the seasonal variations of three photochemical
by-products: C$_{4}$H$_{2}$, C$_{3}$H$_{4}$, and
C$_{2}$N$_{2}$.
Results: We show that the abundances
of these three gases have evolved significantly at northern and southern
high latitudes since 2006. We measure a sudden and steep increase of the
volume mixing ratios of C$_{4}$H$_{2}$,
C$_{3}$H$_{4}$, and C$_{2}$N$_{2}$ at the south
pole from 2012 to 2013, whereas the abundances of these gases remained
approximately constant at the north pole over the same period. At
northern mid-latitudes, C$_{2}$N$_{2}$ and
C$_{4}$H$_{2}$ abundances decrease after 2012 while
C$_{3}$H$_{4}$ abundances stay constant. The comparison of
these volume mixing ratio variations with the predictions of
photochemical and dynamical models provides constraints on the seasonal
evolution of atmospheric circulation and chemical processes at play.
}},
doi = {10.1051/0004-6361/201630255},
adsurl = {https://ui.adsabs.harvard.edu/abs/2018A%26A...609A..64S},
localpdf = {REF/2018A_26A...609A..64S.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2015NatGe...8..362C,
author = {{Charnay}, B. and {Barth}, E. and {Rafkin}, S. and {Narteau}, C. and
{Lebonnois}, S. and {Rodriguez}, S. and {Courrech Du Pont}, S. and
{Lucas}, A.},
title = {{Methane storms as a driver of Titan's dune orientation}},
journal = {Nature Geoscience},
archiveprefix = {arXiv},
eprint = {1504.03404},
primaryclass = {astro-ph.EP},
year = 2015,
volume = 8,
pages = {362-366},
abstract = {{The equatorial regions of Saturn's moon Titan are covered by linear
dunes that propagate eastwards. Global climate models (GCMs), however,
predict westward mean surface winds at low latitudes on Titan, similar
to the trade winds on Earth. This apparent contradiction has been
attributed to Saturn's gravitational tides, large-scale topography and
wind statistics, but none of these hypotheses fully explains the global
eastward propagation of dunes in Titan's equatorial band. However, above
altitudes of about 5 km, Titan's atmosphere is in eastward
super-rotation, suggesting that this momentum may be delivered to the
surface. Here we assess the influence of equatorial tropical methane
storms--which develop at high altitudes during the equinox--on Titan's
dune orientation, using mesoscale simulations of convective methane
clouds with a GCM wind profile that includes super-rotation. We find
that these storms produce fast eastward gust fronts above the surface
that exceed the normal westward surface winds. These episodic gusts
generated by tropical storms are expected to dominate aeolian transport,
leading to eastward propagation of dunes. We therefore suggest a
coupling between super-rotation, tropical methane storms and dune
formation on Titan. This framework, applied to GCM predictions and
analogies to some terrestrial dune fields, explains the linear shape,
eastward propagation and poleward divergence of Titan's dunes, and
implies an equatorial origin of dune sand.
}},
doi = {10.1038/ngeo2406},
adsurl = {https://ui.adsabs.harvard.edu/abs/2015NatGe...8..362C},
localpdf = {REF/2015NatGe...8..362C.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2015Icar..250...95V,
author = {{Vinatier}, S. and {Bézard}, B. and {Lebonnois}, S. and
{Teanby}, N.~A. and {Achterberg}, R.~K. and {Gorius}, N. and
{Mamoutkine}, A. and {Guandique}, E. and {Jolly}, A. and {Jennings}, D.~E. and
{Flasar}, F.~M.},
title = {{Seasonal variations in Titan's middle atmosphere during the northern spring derived from Cassini/CIRS observations}},
journal = {\icarus},
keywords = {Titan, atmosphere, Infrared observations, Atmospheres, structure, Atmospheres, composition},
year = 2015,
volume = 250,
pages = {95-115},
abstract = {{We analyzed spectra acquired at the limb of Titan in the 2006-2013
period by the Cassini/Composite Infrared Spectrometer (CIRS) in order to
monitor the seasonal evolution of the thermal, gas composition and
aerosol spatial distributions. We are primarily interested here in the
seasonal changes after the northern spring equinox and interpret our
results in term of global circulation seasonal changes. Data cover the
600-1500 cm$^{-1}$ spectral range at a resolution of 0.5 or 15.5
cm$^{-1}$ and probe the 150-500 km vertical range with a vertical
resolution of about 30 km. Retrievals of the limb spectra acquired at
15.5 cm$^{-1}$ resolution allowed us to derive eight global maps
of temperature, aerosols and C$_{2}$H$_{2}$,
C$_{2}$H$_{6}$ and HCN molecular mixing ratios between July
2009 and May 2013. In order to have a better understanding of the global
changes taking place after the northern spring equinox, we analyzed 0.5
cm$^{-1}$ resolution limb spectra to infer the mixing ratio
profiles of 10 molecules for some latitudes. These profiles are compared
with CIRS observations performed during the northern winter. Our
observations are compatible with the coexistence of two circulation
cells upwelling at mid-latitudes and downwelling at both poles from at
last January 2010 to at least June 2010. One year later, in June 2011,
there are indications that the global circulation had reversed compared
to the winter situation, with a single pole-to-pole cell upwelling at
the north pole and downwelling at the south pole. Our observations show
that in December 2011, this new pole-to-pole cell has settled with a
downward velocity of 4.4 mm/s at 450 km above the south pole. Therefore,
in about two years after the equinox, the global circulation observed
during the northern winter has totally reversed, which is in agreement
with the predictions of general circulation models. We observe a sudden
unexpected temperature decrease above the south pole in February 2012,
which is probably related to the strong enhancement of molecular gas in
this region, acting as radiative coolers. In July and November 2012, we
observe a detached haze layer located around 320-330 km, which is
comparable to the altitude of the detached haze layer observed by the
Cassini Imaging Science Subsystem (ISS) in the UV.
}},
doi = {10.1016/j.icarus.2014.11.019},
adsurl = {https://ui.adsabs.harvard.edu/abs/2015Icar..250...95V},
localpdf = {REF/2015Icar..250...95V.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2013Icar..223..330G,
author = {{Gans}, B. and {Peng}, Z. and {Carrasco}, N. and {Gauyacq}, D. and
{Lebonnois}, S. and {Pernot}, P.},
title = {{Impact of a new wavelength-dependent representation of methane photolysis branching ratios on the modeling of Titan's atmospheric photochemistry}},
journal = {\icarus},
year = 2013,
volume = 223,
pages = {330-343},
abstract = {{A new wavelength-dependent model for CH$_{4}$ photolysis branching
ratios is proposed, based on the values measured recently by Gans et al.
(Gans, B. et al. [2011]. Phys. Chem. Chem. Phys. 13, 8140-8152). We
quantify the impact of this representation on the predictions of a
photochemical model of Titan's atmosphere, on their precision, and
compare to earlier representations. Although the observed effects on the
mole fraction of the species are small (never larger than 50\%), it is
possible to draw some recommendations for further studies: (i) the
Ly-{$\alpha$} branching ratios of Wang et al. (Wang, J.H. et al. [2000]. J.
Chem. Phys. 113, 4146-4152) used in recent models overestimate the
CH$_{2}$:CH$_{3}$ ratio, a factor to which a lot of species
are sensitive; (ii) the description of out-of-Ly-{$\alpha$} branching
ratios by the ''100\% CH$_{3}$'' scenario has to be avoided, as it
can bias significantly the mole fractions of some important species
(C$_{3}$H$_{8}$); and (iii) complementary experimental data
in the 130-140 nm range would be useful to constrain the models in the
Ly-{$\alpha$} deprived 500-700 km altitude range.
}},
doi = {10.1016/j.icarus.2012.11.024},
adsurl = {http://cdsads.u-strasbg.fr/abs/2013Icar..223..330G},
localpdf = {REF/2013Icar..223..330G.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2012JGRE..11712004L,
author = {{Lebonnois}, S. and {Covey}, C. and {Grossman}, A. and {Parish}, H. and
{Schubert}, G. and {Walterscheid}, R. and {Lauritzen}, P. and
{Jablonowski}, C.},
title = {{Angular momentum budget in General Circulation Models of superrotating atmospheres: A critical diagnostic}},
journal = {Journal of Geophysical Research (Planets)},
keywords = {Atmospheric Composition and Structure: Planetary atmospheres (5210, 5405, 5704), Atmospheric Processes: General circulation (1223), Planetary Sciences: Solid Surface Planets: Atmospheres (0343, 1060), Planetary Sciences: Solar System Objects: Venus},
year = 2012,
volume = 117,
number = e16,
eid = {E12004},
pages = {12004},
abstract = {{To help understand the large disparity in the results of circulation
modeling for the atmospheres of Titan and Venus, where the whole
atmosphere rotates faster than the surface (superrotation), the
atmospheric angular momentum budget is detailed for two General
Circulation Models (GCMs). The LMD GCM is tested for both Venus (with
simplified and with more realistic physical forcings) and Titan
(realistic physical forcings). The Community Atmosphere Model is tested
for both Earth and Venus with simplified physical forcings. These
analyses demonstrate that errors related to atmospheric angular momentum
conservation are significant, especially for Venus when the physical
forcings are simplified. Unphysical residuals that have to be balanced
by surface friction and mountain torques therefore affect the overall
circulation. The presence of topography increases exchanges of angular
momentum between surface and atmosphere, reducing the impact of these
numerical errors. The behavior of GCM dynamical cores with regard to
angular momentum conservation under Venus conditions provides an
explanation of why recent GCMs predict dissimilar results despite
identical thermal forcing. The present study illustrates the need for
careful and detailed analysis of the angular momentum budget for any GCM
used to simulate superrotating atmospheres.
}},
doi = {10.1029/2012JE004223},
adsurl = {http://cdsads.u-strasbg.fr/abs/2012JGRE..11712004L},
localpdf = {REF/2012JGRE..11712004L.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2012P&SS...70...73L,
author = {{Lorenz}, R.~D. and {Newman}, C.~E. and {Tokano}, T. and {Mitchell}, J.~L. and
{Charnay}, B. and {Lebonnois}, S. and {Achterberg}, R.~K.},
title = {{Formulation of a wind specification for Titan late polar summer exploration}},
journal = {\planss},
year = 2012,
volume = 70,
pages = {73-83},
abstract = {{Titan's polar regions, and its hydrocarbon lakes in particular, are of
interest for future exploration. The polar conditions have considerable
seasonal variation and are distinct from the equatorial environment
experienced by Huygens. Thus specific environmental models are required
for these regions. This paper, informed by Cassini and groundbased
observations and four independent Global Circulation Models (GCMs),
summarizes northern summer polar conditions (specifically, regions north
of 65{\deg}N, during the 2023-2024 period, or solar longitude
L$_{s}${\tilde}150$^{o}$-170{\deg}) and presents a simple
analytical formulation of expected, minimum and maximum winds as a
function of altitude to aid spacecraft and instrument design for future
exploration, with particular reference to the descent dispersions of the
Titan Mare Explorer (TiME) mission concept presently under development.
We also consider winds on the surface, noting that these (of relevance
for impact conditions, for waves, and for wind-driven drift of a
floating capsule) are weaker than those in the lowest cell in most GCMs:
some previously-reported estimates of 'surface' wind speeds (actually at
90-500 m altitude) should be reduced by 20-35\% to refer to the standard
10 m 'anemometer height' applicable for surface phenomena. A Weibull
distribution with scale speed C=0.4 m/s and shape parameter k=2.0
embraces the GCM-predicted surface wind speeds.
}},
doi = {10.1016/j.pss.2012.05.015},
adsurl = {http://cdsads.u-strasbg.fr/abs/2012P%26SS...70...73L},
localpdf = {REF/2012P_26SS...70...73L.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2012Icar..218..707L,
author = {{Lebonnois}, S. and {Burgalat}, J. and {Rannou}, P. and {Charnay}, B.
},
title = {{Titan global climate model: A new 3-dimensional version of the IPSL Titan GCM}},
journal = {\icarus},
year = 2012,
volume = 218,
pages = {707-722},
abstract = {{We have developed a new 3-dimensional climate model for Titan's
atmosphere, using the physics of the IPSL Titan 2-dimensional climate
model with the current version of the LMDZ General Circulation Model
dynamical core. Microphysics and photochemistry are still computed as
zonal averages. This GCM covers altitudes from surface to 500 km
altitude, with barotropic waves now being resolved and the diurnal cycle
included. The boundary layer scheme has been changed, yielding a strong
improvement in the tropospheric zonal wind profile modeled at Huygens
descent position and season. The potential temperature profile is fairly
consistent with Huygens observations in the lowest 10 km. The
latitudinal profile of the near-surface temperature is close to observed
values. The minimum of zonal wind observed by the Huygens probe just
above the tropopause is also present in these simulations, and its
origin is discussed by comparing solar heating and dynamical transport
of energy. The stratospheric temperature and wind fields are consistent
with our previous works. Compared to observations, the zonal wind peak
is too weak (around 120 m/s) and too low (around 200 km). The
temperature structures appear to be compressed in altitude, and depart
strongly from observations in the upper stratosphere. These
discrepancies are correlated, and most probably related to the altitude
of the haze production. The model produces a detached haze layer located
more than 150 km lower than observed by the Cassini instruments. This
low production altitude is due to the current position of the GCM upper
boundary. However, the temporal behaviour of the detached haze layer in
the model may explain the seasonal differences observed between Cassini
and Voyager 1. The waves present in the GCM are analyzed, together with
their respective roles in the angular momentum budget. Though the role
of the mean meridional circulation in momentum transport is similar to
previous work, and the transport by barotropic waves is clearly seen in
the stratosphere, a significant part of the transport at high latitudes
is done all year long through low-frequency tropospheric waves that may
be baroclinic waves.
}},
doi = {10.1016/j.icarus.2011.11.032},
adsurl = {http://cdsads.u-strasbg.fr/abs/2012Icar..218..707L},
localpdf = {REF/2012Icar..218..707L.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2012P&SS...61...99C,
author = {{Cordier}, D. and {Mousis}, O. and {Lunine}, J.~I. and {Lebonnois}, S. and
{Rannou}, P. and {Lavvas}, P. and {Lobo}, L.~Q. and {Ferreira}, A.~G.~M.
},
title = {{Titan's lakes chemical composition: Sources of uncertainties and variability}},
journal = {\planss},
archiveprefix = {arXiv},
eprint = {1104.2131},
primaryclass = {astro-ph.EP},
year = 2012,
volume = 61,
pages = {99-107},
abstract = {{Between 2004 and 2007 the instruments of the Cassini spacecraft,
orbiting within the Saturn system, discovered dark patches in the polar
regions of Titan. These features are interpreted as hydrocarbon lakes
and seas with ethane and methane identified as the main compounds. In
this context, we have developed a lake-atmosphere equilibrium model
allowing the determination of the chemical composition of these liquid
areas present on Titan. The model is based on uncertain thermodynamic
data and precipitation rates of organic species predicted to be present
in the lakes and seas that are subject to spatial and temporal
variations. Here we explore and discuss the influence of these
uncertainties and variations. The errors and uncertainties relevant to
thermodynamic data are simulated via Monte Carlo simulations. Global
circulation models (GCM) are also employed in order to investigate the
possibility of chemical asymmetry between the south and the north poles,
due to differences in precipitation rates. We find that mole fractions
of compounds in the liquid phase have a high sensitivity to
thermodynamic data used as inputs, in particular molar volumes and
enthalpies of vaporization. When we combine all considered
uncertainties, the ranges of obtained mole fractions are rather large
(up to {\tilde}8500\%) but the distributions of values are narrow. The
relative standard deviations remain between 10\% and {\tilde}300\%
depending on the compound considered. Compared to other sources of
uncertainties and variability, deviation caused by surface pressure
variations are clearly negligible, remaining of the order of a few
percent up to {\tilde}20\%. Moreover, no significant difference is found
between the composition of lakes located in north and south poles.
Because the theory of regular solutions employed here is sensitive to
thermodynamic data and is not suitable for polar molecules such as HCN
and CH$_{3}$CN, our work strongly underlines the need for
experimental simulations and the improvement of Titan's atmospheric
models.
}},
doi = {10.1016/j.pss.2011.05.009},
adsurl = {http://cdsads.u-strasbg.fr/abs/2012P%26SS...61...99C},
localpdf = {REF/2012P_26SS...61...99C.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2012NatGe...5..106C,
author = {{Charnay}, B. and {Lebonnois}, S.},
title = {{Two boundary layers in Titan's lower troposphere inferred from a climate model}},
journal = {Nature Geoscience},
year = 2012,
volume = 5,
pages = {106-109},
abstract = {{Saturn's moon Titan has a dense atmosphere, but its thermal structure is
poorly known. Conflicting information has been gathered on the nature,
extent and evolution of Titan's planetary boundary layer--the layer of
the atmosphere that is influenced by the surface--from radio-occultation
observations by the Voyager 1 spacecraft and the Cassini orbiter,
measurements by the Huygens probe and by dune-spacing analyses.
Specifically, initial analyses of the Huygens data suggested a boundary
layer of 300m depth with no diurnal evolution, incompatible with
alternative estimates of 2-3km (refs , , ). Here we use a
three-dimensional general circulation model, albeit not explicitly
simulating the methane cycle, to analyse the dynamics leading to the
thermal profile of Titan's lowermost atmosphere. In our simulations, a
convective boundary layer develops in the course of the day, rising to
an altitude of 800m. In addition, a seasonal boundary of 2km depth is
produced by the reversal of the Hadley cell at the equinox, with a
dramatic impact on atmospheric circulation. We interpret fog that had
been discovered at Titan's south pole earlier as boundary layer clouds.
We conclude that Titan's troposphere is well structured, featuring two
boundary layers that control wind patterns, dune spacing and cloud
formation at low altitudes.
}},
doi = {10.1038/ngeo1374},
adsurl = {http://cdsads.u-strasbg.fr/abs/2012NatGe...5..106C},
localpdf = {REF/2012NatGe...5..106C.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2010ApJ...721L.117C,
author = {{Cordier}, D. and {Mousis}, O. and {Lunine}, J.~I. and {Lebonnois}, S. and
{Lavvas}, P. and {Lobo}, L.~Q. and {Ferreira}, A.~G.~M.},
title = {{About the Possible Role of Hydrocarbon Lakes in the Origin of Titan's Noble Gas Atmospheric Depletion}},
journal = {\apjl},
archiveprefix = {arXiv},
eprint = {1008.3712},
primaryclass = {astro-ph.EP},
keywords = {planets and satellites: atmospheres, planets and satellites: individual: Titan, planets and satellites: general},
year = 2010,
volume = 721,
pages = {L117-L120},
abstract = {{An unexpected feature of Titan's atmosphere is the strong depletion in
primordial noble gases revealed by the Gas Chromatograph Mass
Spectrometer aboard the Huygens probe during its descent on 2005 January
14. Although several plausible explanations have already been
formulated, no definitive response to this issue has yet been found.
Here, we investigate the possible sequestration of these noble gases in
the liquid contained in lakes and wet terrains on Titan and the
consequences for their atmospheric abundances. Considering the
atmosphere and the liquid existing on the soil as a whole system, we
compute the abundance of each noble gas relative to nitrogen. To do so,
we make the assumption of thermodynamic equilibrium between the liquid
and the atmosphere, the abundances of the different constituents being
determined via regular solution theory. We find that xenon's atmospheric
depletion can be explained by its dissolution at ambient temperature in
the liquid presumably present on Titan's soil. In the cases of argon and
krypton, we find that the fractions incorporated in the liquid are
negligible, implying that an alternative mechanism must be invoked to
explain their atmospheric depletion.
}},
doi = {10.1088/2041-8205/721/2/L117},
adsurl = {http://cdsads.u-strasbg.fr/abs/2010ApJ...721L.117C},
localpdf = {REF/2010ApJ...721L.117C.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2009ExA....23..893C,
author = {{Coustenis}, A. and {Atreya}, S.~K. and {Balint}, T. and {Brown}, R.~H. and
{Dougherty}, M.~K. and {Ferri}, F. and {Fulchignoni}, M. and
{Gautier}, D. and {Gowen}, R.~A. and {Griffith}, C.~A. and {Gurvits}, L.~I. and
{Jaumann}, R. and {Langevin}, Y. and {Leese}, M.~R. and {Lunine}, J.~I. and
{McKay}, C.~P. and {Moussas}, X. and {M{\"u}ller-Wodarg}, I. and
{Neubauer}, F. and {Owen}, T.~C. and {Raulin}, F. and {Sittler}, E.~C. and
{Sohl}, F. and {Sotin}, C. and {Tobie}, G. and {Tokano}, T. and
{Turtle}, E.~P. and {Wahlund}, J.-E. and {Waite}, J.~H. and
{Baines}, K.~H. and {Blamont}, J. and {Coates}, A.~J. and {Dandouras}, I. and
{Krimigis}, T. and {Lellouch}, E. and {Lorenz}, R.~D. and {Morse}, A. and
{Porco}, C.~C. and {Hirtzig}, M. and {Saur}, J. and {Spilker}, T. and
{Zarnecki}, J.~C. and {Choi}, E. and {Achilleos}, N. and {Amils}, R. and
{Annan}, P. and {Atkinson}, D.~H. and {Bénilan}, Y. and
{Bertucci}, C. and {Bézard}, B. and {Bjoraker}, G.~L. and
{Blanc}, M. and {Boireau}, L. and {Bouman}, J. and {Cabane}, M. and
{Capria}, M.~T. and {Chassefière}, E. and {Coll}, P. and
{Combes}, M. and {Cooper}, J.~F. and {Coradini}, A. and {Crary}, F. and
{Cravens}, T. and {Daglis}, I.~A. and {de Angelis}, E. and {de Bergh}, C. and
{de Pater}, I. and {Dunford}, C. and {Durry}, G. and {Dutuit}, O. and
{Fairbrother}, D. and {Flasar}, F.~M. and {Fortes}, A.~D. and
{Frampton}, R. and {Fujimoto}, M. and {Galand}, M. and {Grasset}, O. and
{Grott}, M. and {Haltigin}, T. and {Herique}, A. and {Hersant}, F. and
{Hussmann}, H. and {Ip}, W. and {Johnson}, R. and {Kallio}, E. and
{Kempf}, S. and {Knapmeyer}, M. and {Kofman}, W. and {Koop}, R. and
{Kostiuk}, T. and {Krupp}, N. and {K{\"u}ppers}, M. and {Lammer}, H. and
{Lara}, L.-M. and {Lavvas}, P. and {Le Mouélic}, S. and
{Lebonnois}, S. and {Ledvina}, S. and {Li}, J. and {Livengood}, T.~A. and
{Lopes}, R.~M. and {Lopez-Moreno}, J.-J. and {Luz}, D. and {Mahaffy}, P.~R. and
{Mall}, U. and {Martinez-Frias}, J. and {Marty}, B. and {McCord}, T. and
{Menor Salvan}, C. and {Milillo}, A. and {Mitchell}, D.~G. and
{Modolo}, R. and {Mousis}, O. and {Nakamura}, M. and {Neish}, C.~D. and
{Nixon}, C.~A. and {Nna Mvondo}, D. and {Orton}, G. and {Paetzold}, M. and
{Pitman}, J. and {Pogrebenko}, S. and {Pollard}, W. and {Prieto-Ballesteros}, O. and
{Rannou}, P. and {Reh}, K. and {Richter}, L. and {Robb}, F.~T. and
{Rodrigo}, R. and {Rodriguez}, S. and {Romani}, P. and {Ruiz Bermejo}, M. and
{Sarris}, E.~T. and {Schenk}, P. and {Schmitt}, B. and {Schmitz}, N. and
{Schulze-Makuch}, D. and {Schwingenschuh}, K. and {Selig}, A. and
{Sicardy}, B. and {Soderblom}, L. and {Spilker}, L.~J. and {Stam}, D. and
{Steele}, A. and {Stephan}, K. and {Strobel}, D.~F. and {Szego}, K. and
{Szopa}, C. and {Thissen}, R. and {Tomasko}, M.~G. and {Toublanc}, D. and
{Vali}, H. and {Vardavas}, I. and {Vuitton}, V. and {West}, R.~A. and
{Yelle}, R. and {Young}, E.~F.},
title = {{TandEM: Titan and Enceladus mission}},
journal = {Experimental Astronomy},
keywords = {TandEM, Titan, Enceladus, Saturnian system, Landing probes},
year = 2009,
volume = 23,
pages = {893-946},
abstract = {{TandEM was proposed as an L-class (large) mission in response to
ESA{\rsquo}s Cosmic Vision 2015-2025 Call, and accepted for further
studies, with the goal of exploring Titan and Enceladus. The mission
concept is to perform in situ investigations of two worlds tied together
by location and properties, whose remarkable natures have been partly
revealed by the ongoing Cassini-Huygens mission. These bodies still hold
mysteries requiring a complete exploration using a variety of vehicles
and instruments. TandEM is an ambitious mission because its targets are
two of the most exciting and challenging bodies in the Solar System. It
is designed to build on but exceed the scientific and technological
accomplishments of the Cassini-Huygens mission, exploring Titan and
Enceladus in ways that are not currently possible (full close-up and in
situ coverage over long periods of time). In the current mission
architecture, TandEM proposes to deliver two medium-sized spacecraft to
the Saturnian system. One spacecraft would be an orbiter with a large
host of instruments which would perform several Enceladus flybys and
deliver penetrators to its surface before going into a dedicated orbit
around Titan alone, while the other spacecraft would carry the Titan in
situ investigation components, i.e. a hot-air balloon
(Montgolfière) and possibly several landing probes to be
delivered through the atmosphere.
}},
doi = {10.1007/s10686-008-9103-z},
adsurl = {http://cdsads.u-strasbg.fr/abs/2009ExA....23..893C},
localpdf = {REF/2009ExA....23..893C.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2008Icar..197..556C,
author = {{Crespin}, A. and {Lebonnois}, S. and {Vinatier}, S. and {Bézard}, B. and
{Coustenis}, A. and {Teanby}, N.~A. and {Achterberg}, R.~K. and
{Rannou}, P. and {Hourdin}, F.},
title = {{Diagnostics of Titan's stratospheric dynamics using Cassini/CIRS data and the 2-dimensional IPSL circulation model}},
journal = {\icarus},
year = 2008,
volume = 197,
pages = {556-571},
abstract = {{The dynamics of Titan's stratosphere is discussed in this study, based
on a comparison between observations by the CIRS instrument on board the
Cassini spacecraft, and results of the 2-dimensional circulation model
developed at the Institute Pierre-Simon Laplace, available at
http://www.lmd.jussieu.fr/titanDbase [Rannou, P., Lebonnois, S.,
Hourdin, F., Luz, D., 2005. Adv. Space Res. 36, 2194-2198]. The
comparison aims at both evaluating the model's capabilities and
interpreting the observations concerning: (1) dynamical and thermal
structure using temperature retrievals from Cassini/CIRS and the
vertical profile of zonal wind at the Huygens landing site obtained by
Huygens/DWE; and (2) vertical and latitudinal profiles of stratospheric
gases deduced from Cassini/CIRS data. The modeled thermal structure is
similar to that inferred from observations (Cassini/CIRS and Earth-based
observations). However, the upper stratosphere (above 0.05 mbar) is
systematically too hot in the 2D-CM, and therefore the stratopause
region is not well represented. This bias may be related to the haze
structure and to misrepresented radiative effects in this region, such
as the cooling effect of hydrogen cyanide (HCN). The 2D-CM produces a
strong atmospheric superrotation, with zonal winds reaching 200 m s
$^{-1}$ at high winter latitudes between 200 and 300 km altitude
(0.1-1 mbar). The modeled zonal winds are in good agreement with
retrieved wind fields from occultation observations, Cassini/CIRS and
Huygens/DWE. Changes to the thermal structure are coupled to changes in
the meridional circulation and polar vortex extension, and therefore
affect chemical distributions, especially in winter polar regions. When
a higher altitude haze production source is used, the resulting modeled
meridional circulation is weaker and the vertical and horizontal mixing
due to the polar vortex is less extended in latitude. There is an
overall good agreement between modeled chemical distributions and
observations in equatorial regions. The difference in observed vertical
gradients of C $_{2}$H $_{2}$ and HCN may be an indicator of
the relative strength of circulation and chemical loss of HCN. The
negative vertical gradient of ethylene in the low stratosphere at
15{\deg} S, cannot be modeled with simple 1-dimensional models, where a
strong photochemical sink in the middle stratosphere would be necessary.
It is explained here by dynamical advection from the winter pole towards
the equator in the low stratosphere and by the fact that ethylene does
not condense. Near the winter pole (80{\deg} N), some compounds (C
$_{4}$H $_{2}$, C $_{3}$H $_{4}$) exhibit an
(interior) minimum in the observed abundance vertical profiles, whereas
2D-CM profiles are well mixed all along the atmospheric column. This
minimum can be a diagnostic of the strength of the meridional
circulation, and of the spatial extension of the winter polar vortex
where strong descending motions are present. In the summer hemisphere,
observed stratospheric abundances are uniform in latitude, whereas the
model maintains a residual enrichment over the summer pole from the
spring cell due to a secondary meridional overturning between 1 and 50
mbar, at latitudes south of 40-50{\deg} S. The strength, as well as
spatial and temporal extensions of this structure are a difficulty, that
may be linked to possible misrepresentation of horizontally mixing
processes, due to the restricted 2-dimensional nature of the model. This
restriction should also be kept in mind as a possible source of other
discrepancies.
}},
doi = {10.1016/j.icarus.2008.05.010},
adsurl = {https://ui.adsabs.harvard.edu/abs/2008Icar..197..556C},
localpdf = {REF/2008Icar..197..556C.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2008Icar..197..110D,
author = {{De La Haye}, V. and {Waite}, J.~H. and {Cravens}, T.~E. and
{Robertson}, I.~P. and {Lebonnois}, S.},
title = {{Coupled ion and neutral rotating model of Titan's upper atmosphere}},
journal = {\icarus},
year = 2008,
volume = 197,
pages = {110-136},
abstract = {{A one-dimensional composition model of Titan's upper atmosphere is
constructed, coupling 36 neutral species and 47 ions. Energy inputs from
the Sun and from Saturn's magnetosphere and updated temperature and eddy
coefficient parameters are taken into account. A rotating technique at
constant latitude and varying local-time is proposed to account for the
diurnal variation of solar inputs. The contributions of
photodissocation, neutral chemistry, ion-neutral chemistry, and electron
recombination to neutral production are presented as a function of
altitude and local time. Local time-dependent mixing ratio and density
profiles are presented in the context of the T and T Cassini data and
are compared in detail to previous models. An independent and simplified
ion and neutral scheme (19-species) is also proposed for future
3D-purposes. The model results demonstrate that a complete understanding
of the chemistry of Titan's upper atmosphere requires an understanding
of the coupled ion and neutral chemistry. In particular, the ionospheric
chemistry makes significant contributions to production rates of several
important neutral species.
}},
doi = {10.1016/j.icarus.2008.03.022},
adsurl = {https://ui.adsabs.harvard.edu/abs/2008Icar..197..110D},
localpdf = {REF/2008Icar..197..110D.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2008Icar..194..201S,
author = {{Sekine}, Y. and {Lebonnois}, S. and {Imanaka}, H. and {Matsui}, T. and
{Bakes}, E.~L.~O. and {McKay}, C.~P. and {Khare}, B.~N. and
{Sugita}, S.},
title = {{The role of organic haze in Titan's atmospheric chemistry. II. Effect of heterogeneous reaction to the hydrogen budget and chemical composition of the atmosphere}},
journal = {\icarus},
year = 2008,
volume = 194,
pages = {201-211},
abstract = {{One of the key components controlling the chemical composition and
climatology of Titan's atmosphere is the removal of reactive atomic
hydrogen from the atmosphere. A proposed process of the removal of
atomic hydrogen is the heterogeneous reaction with organic aerosol. In
this study, we investigate the effect of heterogeneous reactions in
Titan's atmospheric chemistry using new measurements of the
heterogeneous reaction rate [Sekine, Y., Imanaka, H., Matsui, T., Khare,
B.N., Bakes, E.L.O., McKay, C.P., Sugita, S., 2008. Icarus 194, 186-200]
in a one-dimensional photochemical model. Our results indicate that
60-75\% of the atomic hydrogen in the stratosphere and mesosphere are
consumed by the heterogeneous reactions. This result implies that the
heterogeneous reactions on the aerosol surface may predominantly remove
atomic hydrogen in Titan's stratosphere and mesosphere. The results of
our calculation also indicate that a low concentration of atomic
hydrogen enhances the concentrations of unsaturated complex organics,
such as C $_{4}$H $_{2}$ and phenyl radical, by more than
two orders in magnitude around 400 km in altitude. Such an increase in
unsaturated species may induce efficient haze production in Titan's
mesosphere and upper stratosphere. These results imply a positive
feedback mechanism in haze production in Titan's atmosphere. The
increase in haze production would affect the chemical composition of the
atmosphere, which might induce further haze production. Such a positive
feedback could tend to dampen the loss and supply cycles of CH
$_{4}$ due to an episodic CH $_{4}$ release into Titan's
atmosphere.
}},
doi = {10.1016/j.icarus.2007.08.030},
adsurl = {https://ui.adsabs.harvard.edu/abs/2008Icar..194..201S},
localpdf = {REF/2008Icar..194..201S.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2007Icar..191..236D,
author = {{De La Haye}, V. and {Waite}, J.~H. and {Cravens}, T.~E. and
{Nagy}, A.~F. and {Johnson}, R.~E. and {Lebonnois}, S. and {Robertson}, I.~P.
},
title = {{Titan's corona: The contribution of exothermic chemistry}},
journal = {\icarus},
year = 2007,
volume = 191,
pages = {236-250},
abstract = {{The contribution of exothermic ion and neutral chemistry to Titan's
corona is studied. The production rates for fast neutrals N
$_{2}$, CH $_{4}$, H, H $_{2}$, $^{3}$CH
$_{2}$, CH $_{3}$, C $_{2}$H $_{4}$, C
$_{2}$H $_{5}$, C $_{2}$H $_{6}$, N(
$^{4}$S), NH, and HCN are determined using a coupled ion and
neutral model of Titan's upper atmosphere. After production, the
formation of the suprathermal particles is modeled using a two-stream
simulation, as they travel simultaneously through a thermal mixture of N
$_{2}$, CH $_{4}$, and H $_{2}$. The resulting
suprathermal fluxes, hot density profiles, and energy distributions are
compared to the N $_{2}$ and CH $_{4}$ INMS exospheric data
presented in [De La Haye, V., Waite Jr., J.H., Johnson, R.E., Yelle,
R.V., Cravens, T.E., Luhmann, J.G., Kasprzak, W.T., Gell, D.A., Magee,
B., Leblanc, F., Michael, M., Jurac, S., Robertson, I.P., 2007. J.
Geophys. Res., doi:10.1029/2006JA012222, in press], and are found
insufficient for producing the suprathermal populations measured. Global
losses of nitrogen atoms and carbon atoms in all forms due to exothermic
chemistry are estimated to be 8.3{\times}10 Ns and 7.2{\times}10 Cs.
}},
doi = {10.1016/j.icarus.2007.04.031},
adsurl = {https://ui.adsabs.harvard.edu/abs/2007Icar..191..236D},
localpdf = {REF/2007Icar..191..236D.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2006A&A...456..761H,
author = {{Hirtzig}, M. and {Coustenis}, A. and {Gendron}, E. and {Drossart}, P. and
{Negr{\~a}o}, A. and {Combes}, M. and {Lai}, O. and {Rannou}, P. and
{Lebonnois}, S. and {Luz}, D.},
title = {{Monitoring atmospheric phenomena on Titan}},
journal = {\aap},
keywords = {planets and satellites: individual: Titan, instrumentation: adaptive optics},
year = 2006,
volume = 456,
pages = {761-774},
abstract = {{For the past 8 years (1998-2005), we have used adaptive optics imaging
(with VLT/NACO and CFHT/PUEO) to explore Titan's atmosphere, which is
currently scrutinized in situ by the Cassini-Huygens mission. In the
course of our work, we have found variations, such as as seasonal and
diurnal effects, as well as temporary features in the southern polar
region. The north-south asymmetry is shown to have changed since 2000 in
the near-IR and to be currently organized in a brighter northern than
southern pole. We study this evolution here. With our data, we also have
new significant statistical evidence of diurnal effects in Titan's
stratosphere, with a brighter (as much as 19\%) morning limb appearing in
our images in many cases, when the phase effect is expected on the
evening side. The southern bright feature is probably a time-limited
seasonal and/or meteorological phenomenon, revolving around the south
pole (confined in its motion within the 80{\deg}S parallel) and located
somewhere in the upper troposphere (18-40 km of altitude). Its behavior
and possible nature are discussed here.
}},
doi = {10.1051/0004-6361:20053381},
adsurl = {https://ui.adsabs.harvard.edu/abs/2006A%26A...456..761H},
localpdf = {REF/2006A_26A...456..761H.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2006Sci...311..201R,
author = {{Rannou}, P. and {Montmessin}, F. and {Hourdin}, F. and {Lebonnois}, S.
},
title = {{The Latitudinal Distribution of Clouds on Titan}},
journal = {Science},
year = 2006,
volume = 311,
pages = {201-205},
abstract = {{Clouds have been observed recently on Titan, through the thick haze,
using near-infrared spectroscopy and images near the south pole and in
temperate regions near 40{\deg}S. Recent telescope and Cassini orbiter
observations are now providing an insight into cloud climatology. To
study clouds, we have developed a general circulation model of Titan
that includes cloud microphysics. We identify and explain the formation
of several types of ethane and methane clouds, including south polar
clouds and sporadic clouds in temperate regions and especially at
40{\deg} in the summer hemisphere. The locations, frequencies, and
composition of these cloud types are essentially explained by the
large-scale circulation.
}},
doi = {10.1126/science.1118424},
adsurl = {https://ui.adsabs.harvard.edu/abs/2006Sci...311..201R},
localpdf = {REF/2006Sci...311..201R.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2005P&SS...53..486L,
author = {{Lebonnois}, S.},
title = {{Benzene and aerosol production in Titan and Jupiter's atmospheres: a sensitivity study}},
journal = {\planss},
year = 2005,
volume = 53,
pages = {486-497},
abstract = {{Benzene has recently been observed in the atmosphere of Jupiter, Saturn
and also Titan. This compound is required as a precursor for larger
aromatic species (PAHs) that may be part of aerosol particles. Several
photochemical models have tried to reproduce the observed quantities of
benzene in the atmospheres of Jupiter (both low- and high-latitudes
regions), Saturn and Titan. In this present work, we have conducted a
sensitivity study of benzene and PAHs formation, using similar
photochemical schemes both for Titan and Jupiter (low-latitudes
conditions). Two different photochemical schemes are used, for which the
modeled composition fairly agrees with observational constraints, both
for Jupiter and Titan. Some disagreements are specific to each
atmospheric case, which may point to needed improvements, especially in
kinetic data involved in the corresponding chemical cycles. The observed
benzene mole fraction in Titan's stratosphere is reproduced by the
model, but in the case of Jupiter, low-latitudes benzene abundance is
only 3\% of the observed column density, which may indicate a possible
influence of latitudinal transport, since abundance of benzene is much
higher in auroral regions. Though, the photochemical scheme of
C$_{6}$ compounds at temperature and pressure conditions of
planetary atmospheres is still very uncertain. Several variations are
therefore done on key reactions in benzene production. These variations
show that benzene abundance is mainly sensitive to reactions that may
affect the propargyl radical. The effect of aerosol production on
hydrocarbons composition is also tested, as well as possible
heterogenous recombination of atomic hydrogen in the case of Titan. PAHs
are a major pathway for aerosol production in both models. The mass
production profiles for aerosols are discussed for both Titan and
Jupiter. Total production mass fluxes are roughly three times the one
expected by observational constraints in both cases. Such comparative
studies are useful to bring more constraints on photochemical models.
}},
doi = {10.1016/j.pss.2004.11.004},
adsurl = {https://ui.adsabs.harvard.edu/abs/2005P%26SS...53..486L},
localpdf = {REF/2005P_26SS...53..486L.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2005AdSpR..36.2194R,
author = {{Rannou}, P. and {Lebonnois}, S. and {Hourdin}, F. and {Luz}, D.
},
title = {{Titan atmosphere database}},
journal = {Advances in Space Research},
year = 2005,
volume = 36,
pages = {2194-2198},
abstract = {{We have developed in the last decade a two-dimensional version of the
Titan global circulation model LMDZ. This model accounts for multiple
coupling occuring on Titan between dynamics, haze, chemistry and
radiative transfer. It was successful at explaining many observed
features related to atmosphere state (wind, temperature), haze structure
and chemical species distributions, recently, an important step in our
knowledge about Titan has been done with Cassini and Huygens visits to
Titan. In this context, we want to make the results of our model
available for the scientific community which is involved in the study of
Titan. Such a tool should be useful to give a global frame (spatial and
time behaviour of physical quantities) for interpreting ground based
telescope observations.
}},
doi = {10.1016/j.asr.2005.09.041},
adsurl = {https://ui.adsabs.harvard.edu/abs/2005AdSpR..36.2194R},
localpdf = {REF/2005AdSpR..36.2194R.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2004JGRE..10912005H,
author = {{Hourdin}, F. and {Lebonnois}, S. and {Luz}, D. and {Rannou}, P.
},
title = {{Titan's stratospheric composition driven by condensation and dynamics}},
journal = {Journal of Geophysical Research (Planets)},
keywords = {Planetology: Fluid Planets: Atmospheres-structure and dynamics, Planetology: Fluid Planets: Atmospheres-composition and chemistry, Planetology: Solar System Objects: Saturnian satellites},
year = 2004,
volume = 109,
number = e18,
eid = {E12005},
pages = {12005},
abstract = {{Atmospheric transport of chemical compounds and organic haze in the
stratosphere of Titan is investigated with an axisymmetric general
circulation model. It has been shown previously that the meridional
circulation, dominated by global Hadley cells, is responsible both for
the creation of an intense stratospheric zonal flow and for the
accumulation of chemical compounds and haze in high latitudes. The
modified composition in turn intensifies the meridional circulation and
equator-to-pole thermal contrasts. This paper analyzes in detail the
transport processes responsible for the observed vertical and
latitudinal variations of atmospheric composition. It is shown that the
competition between rapid sinking of air from the upper stratosphere in
the winter polar vortex and latitudinal mixing by barotropic planetary
waves (parameterized in the model) controls the vertical gradient of
chemical compounds. The magnitude of polar enrichment (of a factor 1.4
to 20 depending on the particular species) with respect to low latitudes
is mostly controlled by the way the meridional advection increases the
concentrations of chemical compounds in the clean air which is rising
from the troposphere, where most of the chemical compounds are removed
by condensation (the temperature at the tropopause being close to 70 K).
The agreement between the observed and simulated contrasts provides an
indirect but strong validation of the simulated dynamics, thus
confirming the explanation put forward for atmospheric superrotation. It
is shown also that by measuring the atmospheric composition, the
Cassini-Huygens mission will provide a strong constraint about Titan's
atmospheric circulation.
}},
doi = {10.1029/2004JE002282},
adsurl = {https://ui.adsabs.harvard.edu/abs/2004JGRE..10912005H},
localpdf = {REF/2004JGRE..10912005H.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2003Icar..166..343L,
author = {{Luz}, D. and {Hourdin}, F. and {Rannou}, P. and {Lebonnois}, S.
},
title = {{Latitudinal transport by barotropic waves in Titan's stratosphere.. II. Results from a coupled dynamics-microphysics-photochemistry GCM}},
journal = {\icarus},
year = 2003,
volume = 166,
pages = {343-358},
abstract = {{We present a 2D general circulation model of Titan's atmosphere,
coupling axisymmetric dynamics with haze microphysics, a simplified
photochemistry and eddy mixing. We develop a parameterization of
latitudinal eddy mixing by barotropic waves based on a shallow-water,
longitude-latitude model. The parameterization acts locally and in real
time both on passive tracers and momentum. The mixing coefficient varies
exponentially with a measure of the barotropic instability of the mean
zonal flow. The coupled GCM approximately reproduces the Voyager
temperature measurements and the latitudinal contrasts in the
distributions of HCN and C $_{2}$H $_{2}$, as well as the
main features of the zonal wind retrieved from the 1989 stellar
occultation. Wind velocities are consistent with the observed reversal
time of the North-South albedo asymmetry of 5 terrestrial years. Model
results support the hypothesis of a non-uniform distribution of infrared
opacity as the cause of the Voyager temperature asymmetry. Transport by
the mean meridional circulation, combined with polar vortex isolation
may be at the origin of the latitudinal contrasts of trace species, with
eddy mixing remaining restricted to low latitudes most of the Titan
year. We interpret the contrasts as a signature of non-axisymmetric
motions.
}},
doi = {10.1016/j.icarus.2003.08.014},
adsurl = {https://ui.adsabs.harvard.edu/abs/2003Icar..166..343L},
localpdf = {REF/2003Icar..166..343L.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2003Icar..163..164L,
author = {{Lebonnois}, S. and {Hourdin}, F. and {Rannou}, P. and {Luz}, D. and
{Toublanc}, D.},
title = {{Impact of the seasonal variations of composition on the temperature field of Titan's stratosphere}},
journal = {\icarus},
year = 2003,
volume = 163,
pages = {164-174},
abstract = {{We investigate the role of seasonal variations of Titan's stratospheric
composition on the temperature. We use a general circulation model
coupled with idealized chemical tracers that reproduce variations of
ethane (C $_{2}$H $_{6}$), acetylene (C $_{2}$H
$_{2}$), and hydrogen cyanide (HCN). Enhancement of the mole
fractions of these compounds, at high latitudes in the winter hemisphere
relative to their equatorial values, induces a relative decrease in
temperature above approximately 0.2 mbar, with a peak amplitude around
-20 K, and a relative increase in temperature below, around 1 mbar, with
a peak amplitude around +7 K. These thermal effects are mainly due to
the variations of the cooling to space induced by the varying
distributions. The ethane, acetylene, and hydrogen cyanide variations
affect the cooling rates in a similar way, with the dominant effect
being due to ethane, though its latitudinal variations are small.
}},
doi = {10.1016/S0019-1035(03)00074-5},
adsurl = {https://ui.adsabs.harvard.edu/abs/2003Icar..163..164L},
localpdf = {REF/2003Icar..163..164L.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2003Icar..161..474L,
author = {{Lebonnois}, S. and {Bakes}, E.~L.~O. and {McKay}, C.~P.
},
title = {{Atomic and molecular hydrogen budget in Titan's atmosphere}},
journal = {\icarus},
year = 2003,
volume = 161,
pages = {474-485},
abstract = {{Using a one-dimensional model, we investigate the hydrogen budget and
escape to space in Titan's atmosphere. Our goal is to study in detail
the distributions and fluxes of atomic and molecular hydrogen in the
model, while identifying sources of qualitative and quantitative
uncertainties. Our study confirms that the escape of atomic and
molecular hydrogen to space is limited by the diffusion through the
homopause level. The H distribution and flux inside the atmosphere are
very sensitive to the eddy diffusion coefficient used above altitude 600
km. We chose a high value of this coefficient 1 {\times} 10 $^{8}$
cm $^{2}$ s $^{-1}$ and a homopause level around altitude
900 km. We find that H flows down significantly from the production
region above 500 km to the region [300-500] km, where it recombines into
H $_{2}$. Production of both H and H $_{2}$ also occurs in
the stratosphere, mostly from photodissociation of acetylene. The only
available observational data to be compared are the escape rate of H
deduced from Pioneer 11 and IUE observations of the H torus 1-3 {\times}
10 $^{9}$ cm $^{-2}$ s $^{-1}$ and the latest
retrieved value of the H $_{2}$ mole fraction in the stratosphere:
(1.1 {\plusmn} 0.1) {\times} 10 $^{-3}$. Our results for both of
these values are at least 50-100\% higher, though the uncertainties
within the chemical schemes and other aspects of the model are large.
The chemical conversion from H to H $_{2}$ is essentially done
through catalytic cycles using acetylene and diacetylene. We have
studied the role of this diacetylene cycle, for which the associated
reaction rates are poorly known. We find that it mostly affects C
$_{4}$ species and benzene in the lower atmosphere, rather than
the H profile and the hydrogen budget. We have introduced the
heterogenous recombination of hydrogen on the surface of aerosol
particles in the stratosphere, and this appears to be a significant
process, comparable to the chemical processes. It has a major influence
on the H distribution, and consequently on several other species,
especially C $_{3}$H $_{4}$, C $_{4}$H $_{2}$
and C $_{6}$H $_{6}$. Therefore, this heterogenous process
should be taken into account when trying to understand the stratospheric
distribution of these hydrocarbons.
}},
doi = {10.1016/S0019-1035(02)00039-8},
adsurl = {https://ui.adsabs.harvard.edu/abs/2003Icar..161..474L},
localpdf = {REF/2003Icar..161..474L.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2003Icar..161..468B,
author = {{Bakes}, E.~L.~O. and {Lebonnois}, S. and {Bauschlicher}, C.~W. and
{McKay}, C.~P.},
title = {{The role of submicrometer aerosols and macromolecules in H $_{2}$ formation in the titan haze}},
journal = {\icarus},
year = 2003,
volume = 161,
pages = {468-473},
abstract = {{Previous studies of the photochemistry of small molecules in Titan's
atmosphere found it difficult to have hydrogen atoms removed at a rate
sufficient to explain the observed abundance of unsaturated
hydrocarbons. One qualitative explanation of the discrepancy nominated
catalytic aerosol surface chemistry as an efficient sink of hydrogen
atoms, although no quantitative study of this mechanism was attempted.
In this paper, we quantify how haze aerosols and macromolecules may
efficiently catalyze the formation of hydrogen atoms into H
$_{2}$. We describe the prompt reaction model for the formation of
H $_{2}$ on aerosol surfaces and compare this with the catalytic
formation of H $_{2}$ using negatively charged hydrogenated
aromatic macromolecules. We conclude that the PRM is an efficient
mechanism for the removal of hydrogen atoms from the atmosphere to form
H $_{2}$ with a peak formation rate of {\tilde} 70 cm $^{-3}$
s $^{-1}$ at 420 km. We also conclude that catalytic H
$_{2}$ formation via hydrogenated anionic macromolecules is viable
but much less productive (a maximum of {\tilde} 0.1 cm $^{-3}$ s
$^{-1}$ at 210 km) than microphysical aerosols.
}},
doi = {10.1016/S0019-1035(02)00040-4},
adsurl = {https://ui.adsabs.harvard.edu/abs/2003Icar..161..468B},
localpdf = {REF/2003Icar..161..468B.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2002Icar..159..505L,
author = {{Lebonnois}, S. and {Bakes}, E.~L.~O. and {McKay}, C.~P.},
title = {{Transition from Gaseous Compounds to Aerosols in Titan's Atmosphere}},
journal = {\icarus},
year = 2002,
volume = 159,
pages = {505-517},
abstract = {{We investigate the chemical transition of simple molecules like C
$_{2}$H $_{2}$ and HCN into aerosol particles in the context
of Titan's atmosphere. Experiments that synthesize analogs (tholins) for
these aerosols can help illuminate and constrain these polymerization
mechanisms. Using information available from these experiments, we
suggest chemical pathways that can link simple molecules to
macromolecules, which will be the precursors to aerosol particles:
polymers of acetylene and cyanoacetylene, polycyclic aromatics, polymers
of HCN and other nitriles, and polyynes. Although our goal here is not
to build a detailed kinetic model for this transition, we propose
parameterizations to estimate the production rates of these
macromolecules, their C/N and C/H ratios, and the loss of parent
molecules (C $_{2}$H $_{2}$, HCN, HC $_{3}$N and other
nitriles, and C $_{6}$H $_{6}$) from the gas phase to the
haze. We use a one-dimensional photochemical model of Titan's atmosphere
to estimate the formation rate of precursor macromolecules. We find a
production zone slightly lower than 200 km altitude with a total
production rate of 4{\times}10 $^{-14}$ g cm $^{-2}$ s
$^{-1}$ and a C/N{\sime}4. These results are compared with
experimental data, and to microphysical model requirements. The
Cassini/Huygens mission will bring a detailed picture of the haze
distribution and properties, which will be a great challenge for our
understanding of these chemical processes.
}},
doi = {10.1006/icar.2002.6943},
adsurl = {https://ui.adsabs.harvard.edu/abs/2002Icar..159..505L},
localpdf = {REF/2002Icar..159..505L.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2001Icar..152..384L,
author = {{Lebonnois}, S. and {Toublanc}, D. and {Hourdin}, F. and {Rannou}, P.
},
title = {{Seasonal Variations of Titan's Atmospheric Composition}},
journal = {\icarus},
year = 2001,
volume = 152,
pages = {384-406},
abstract = {{In order to investigate seasonal variations of the composition of
Titan's low stratosphere, we developed a two-dimensional
(latitude-altitude) photochemical and transport model. Large-scale
advection, hidden in the vertical eddy diffusion for one-dimensional
models, is accounted for explicitly. Atmospheric dynamics is prescribed
using results of independent numerical simulations of the atmospheric
general circulation. Both the mean meridional transport and latitudinal
mixing by transient planetary waves are taken into account. Chemistry is
based on 284 reactions involving 40 hydrocarbons and nitriles.
Photodissociation rates are based on a three-dimensional description of
the ultraviolet flux. For most species, the model fits well the
latitudinal variations observed by Voyager I giving for the first time a
full and self-consistent interpretation of these observations. In
particular, the enrichment of the high northern latitudes is attributed
to subsidence during the winter preceeding the Voyager encounter.
Discrepancies are observed for C $_{2}$H $_{4}$, HC
$_{3}$N, and C $_{2}$N $_{2}$ and are attributed to
problems in the chemical scheme. Sensitivity to dynamical parameters is
investigated. The vertical eddy diffusion coefficient keeps an important
role for the upper atmosphere. The wind strength and horizontal eddy
diffusion strongly control the latitudinal behavior of the composition
in the low stratosphere, while mean concentrations appear to be
essentially controlled by chemistry.
}},
doi = {10.1006/icar.2001.6632},
adsurl = {https://ui.adsabs.harvard.edu/abs/2001Icar..152..384L},
localpdf = {REF/2001Icar..152..384L.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{1999JGR...10422025L,
author = {{Lebonnois}, S. and {Toublanc}, D.},
title = {{Actinic fluxes in Titan's atmosphere, from one to three dimensions: Application to high-latitude composition}},
journal = {\jgr},
keywords = {Planetology: Solid Surface Planets, Planetology: Solid Surface Planets: Atmospheres-composition and chemistry, Planetology: Solar System Objects: Saturnian satellites},
year = 1999,
volume = 104,
pages = {22025-22034},
abstract = {{We present a study on diurnally and annually averaged values of the
actinic fluxes used in one-dimensional (1-D) photochemical models, as
well as a 3-D radiative transfer model, based on Monte Carlo
calculations with application to the atmosphere of Titan. This study
shows that the commonly used value {\lt}{\thetas}{\gt}=30{\deg} for the mean
incident angle at the equator in photochemical models of Titan is not
the best choice, though changing the value has no dramatic effects on
photochemistry. The results of the 3-D code give direct access to the
photolysis rates at any point in the atmosphere. The necessity of 3-D
values in a deep atmosphere such as Titan's is demonstrated particularly
for high-latitude winter conditions. These 3-D photolysis rates are used
to model the latitudinal variations of the chemical composition of
Titan's atmosphere in a 1-D photochemical model adapted to different
latitudes. This study shows that these kinds of simple photochemical
models cannot reproduce the observed latitudinal behavior and that we
need to develop real 2-D photochemical models of Titan's atmosphere.
}},
doi = {10.1029/1999JE001056},
adsurl = {https://ui.adsabs.harvard.edu/abs/1999JGR...10422025L},
localpdf = {REF/1999JGR...10422025L.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}