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@comment{{Command line: /usr/bin/bib2bib --quiet -c 'not journal:"Discussions"' -c year=2018 -c $type="ARTICLE" -oc pub2018.txt -ob pub2018.bib}}
  author = {{Bertrand}, T. and {Forget}, F. and {Umurhan}, O.~M. and {Grundy}, W.~M. and 
	{Schmitt}, B. and {Protopapa}, S. and {Zangari}, A.~M. and {White}, O.~L. and 
	{Schenk}, P.~M. and {Singer}, K.~N. and {Stern}, A. and {Weaver}, H.~A. and 
	{Young}, L.~A. and {Ennico}, K. and {Olkin}, C.~B.},
  title = {{The nitrogen cycles on Pluto over seasonal and astronomical timescales}},
  journal = {\icarus},
  archiveprefix = {arXiv},
  eprint = {1804.02434},
  primaryclass = {astro-ph.EP},
  keywords = {Pluto, Nitrogen, Paleo, Modeling, GCM, Sputnik Planitia},
  year = 2018,
  volume = 309,
  pages = {277-296},
  abstract = {{Pluto's landscape is shaped by the endless condensation and sublimation
cycles of the volatile ices covering its surface. In particular, the
Sputnik Planitia ice sheet, which is thought to be the main reservoir of
nitrogen ice, displays a large diversity of terrains, with bright and
dark plains, small pits and troughs, topographic depressions and
evidences of recent and past glacial flows. Outside Sputnik Planitia,
New Horizons also revealed numerous nitrogen ice deposits, in the
eastern side of Tombaugh Regio and at mid-northern latitudes.

These observations suggest a complex history involving volatile and
glacial processes occurring on different timescales. We present
numerical simulations of volatile transport on Pluto performed with a
model designed to simulate the nitrogen cycle over millions of years,
taking into account the changes of obliquity, solar longitude of
perihelion and eccentricity as experienced by Pluto. Using this model,
we first explore how the volatile and glacial activity of nitrogen
within Sputnik Planitia has been impacted by the diurnal, seasonal and
astronomical cycles of Pluto. Results show that the obliquity dominates
the N$_{2}$ cycle and that over one obliquity cycle, the latitudes
of Sputnik Planitia between 25{\deg}S-30{\deg}N are dominated by
N$_{2}$ condensation, while the northern regions between 30{\deg}N
and -50{\deg}N are dominated by N$_{2}$ sublimation. We find that a
net amount of 1 km of ice has sublimed at the northern edge of Sputnik
Planitia during the last 2 millions of years. It must have been
compensated by a viscous flow of the thick ice sheet. By comparing these
results with the observed geology of Sputnik Planitia, we can relate the
formation of the small pits and the brightness of the ice at the center
of Sputnik Planitia to the sublimation and condensation of ice occurring
at the annual timescale, while the glacial flows at its eastern edge and
the erosion of the water ice mountains all around the ice sheet are
instead related to the astronomical timescale. We also perform
simulations including a glacial flow scheme which shows that the Sputnik
Planitia ice sheet is currently at its minimum extent at the northern
and southern edges. We also explore the stability of N$_{2}$ ice
deposits outside the latitudes and longitudes of the Sputnik Planitia
basin. Results show that N$_{2}$ ice is not stable at the poles
but rather in the equatorial regions, in particular in depressions,
where thick deposits may persist over tens of millions of years, before
being trapped in Sputnik Planitia. Finally, another key result is that
the minimum and maximum surface pressures obtained over the simulated
millions of years remain in the range of milli-Pascals and Pascals,
respectively. This suggests that Pluto never encountered conditions
allowing liquid nitrogen to flow directly on its surface. Instead, we
suggest that the numerous geomorphological evidences of past liquid flow
observed on Pluto's surface are the result of liquid nitrogen that
flowed at the base of thick ancient nitrogen glaciers, which have since
  doi = {10.1016/j.icarus.2018.03.012},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Koskinen}, T.~T. and {Guerlet}, S.},
  title = {{Atmospheric structure and helium abundance on Saturn from Cassini/UVIS and CIRS observations}},
  journal = {\icarus},
  keywords = {Saturn, Occultations, Infrared observations, Atmospheres, Structure},
  year = 2018,
  volume = 307,
  pages = {161-171},
  abstract = {{We combine measurements from stellar occultations observed by the
Cassini Ultraviolet Imaging Spectrograph (UVIS) and limb scans observed
by the Composite Infrared Spectrometer (CIRS) to create empirical
atmospheric structure models for Saturn corresponding to the locations
probed by the occultations. The results cover multiple locations at low
to mid-latitudes between the spring of 2005 and the fall of 2015. We
connect the temperature-pressure (T-P) profiles retrieved from the CIRS
limb scans in the stratosphere to the T-P profiles in the thermosphere
retrieved from the UVIS occultations. We calculate the altitudes
corresponding to the pressure levels in each case based on our best fit
composition model that includes H$_{2}$, He, CH$_{4}$ and
upper limits on H. We match the altitude structure to the density
profile in the thermosphere that is retrieved from the occultations. Our
models depend on the abundance of helium and we derive a volume mixing
ratio of 11  {\plusmn}  2\% for helium in the lower atmosphere based on a
statistical analysis of the values derived for 32 different occultation
locations. We also derive the mean temperature and methane profiles in
the upper atmosphere and constrain their variability. Our results are
consistent with enhanced heating at the polar auroral region and a
dynamically active upper atmosphere.
  doi = {10.1016/j.icarus.2018.02.020},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Tran}, H. and {Turbet}, M. and {Chelin}, P. and {Landsheere}, X.
  title = {{Measurements and modeling of absorption by CO$_{2 }$+ H$_{2}$O mixtures in the spectral region beyond the CO$_{2}$ {$\nu$}$_{3}$-band head}},
  journal = {\icarus},
  archiveprefix = {arXiv},
  eprint = {1802.01352},
  primaryclass = {astro-ph.EP},
  year = 2018,
  volume = 306,
  pages = {116-121},
  abstract = {{In this work, we measured the absorption by CO$_{2 }$+
H$_{2}$O mixtures from 2400 to 2600 cm$^{-1}$ which
corresponds to the spectral region beyond the {$\nu$}$_{3}$ band head
of CO$_{2}$. Transmission spectra of CO$_{2}$ mixed with
water vapor were recorded with a high-resolution Fourier-transform
spectrometer for various pressure, temperature and concentration
conditions. The continuum absorption by CO$_{2}$ due to the
presence of water vapor was determined by subtracting from measured
spectra the contribution of local lines of both species, that of the
continuum of pure CO$_{2}$ as well as of the self- and
CO$_{2}$-continua of water vapor induced by the
H$_{2}$O-H$_{2}$O and H$_{2}$O-CO$_{2}$
interactions. The obtained results are in very good agreement with the
unique previous measurement (in a narrower spectral range). They confirm
that the H$_{2}$O-continuum of CO$_{2}$ is significantly
larger than that observed for pure CO$_{2}$. This continuum thus
must be taken into account in radiative transfer calculations for media
involving CO$_{2}$+ H$_{2}$O mixture. An empirical model,
using sub-Lorentzian line shapes based on some temperature-dependent
correction factors {$\chi$} is proposed which enables an accurate
description of the experimental results.
  doi = {10.1016/j.icarus.2018.02.009},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Fernandez-Cascales}, L. and {Lucas}, A. and {Rodriguez}, S. and 
	{Gao}, X. and {Spiga}, A. and {Narteau}, C.},
  title = {{First quantification of relationship between dune orientation and sediment availability, Olympia Undae, Mars}},
  journal = {Earth and Planetary Science Letters},
  keywords = {Mars, dunes, bedform alignment, sediment cover, aeolian transport},
  year = 2018,
  volume = 489,
  pages = {241-250},
  abstract = {{Dunes provide unique information about wind regimes on planetary bodies
where there is no direct meteorological data. At the eastern margin of
Olympia Undae on Mars, dune orientation is measured from satellite
imagery and sediment cover is estimated using the high contrast between
the dune material and substrate. The analysis of these data provide the
first quantification of relationship between sediment availability and
dune orientation. Abrupt and smooth dune reorientations are associated
with inward and outward dynamics of dunes approaching and ejecting from
major sedimentary bodies, respectively. These reorientation patterns
along sediment transport pathways are interpreted using a new generation
dune model based on the coexistence of two dune growth mechanisms. This
model also permits solving of the inverse problem of predicting the wind
regime from dune orientation. For bidirectional wind regimes, solutions
of this inverse problem show substantial differences in the
distributions of sediment flux orientation, which can be attributed to
atmospheric flow variations induced by changes in albedo at the
boundaries of major dune fields. Then, we conclude that relationships
between sediment cover and dune orientation can be used to constrain
wind regime and dune field development on Mars and other planetary
  doi = {10.1016/j.epsl.2018.03.001},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Korablev}, O. and {Montmessin}, F. and {Trokhimovskiy}, A. and 
	{Fedorova}, A.~A. and {Shakun}, A.~V. and {Grigoriev}, A.~V. and 
	{Moshkin}, B.~E. and {Ignatiev}, N.~I. and {Forget}, F. and 
	{Lefèvre}, F. and {Anufreychik}, K. and {Dzuban}, I. and 
	{Ivanov}, Y.~S. and {Kalinnikov}, Y.~K. and {Kozlova}, T.~O. and 
	{Kungurov}, A. and {Makarov}, V. and {Martynovich}, F. and {Maslov}, I. and 
	{Merzlyakov}, D. and {Moiseev}, P.~P. and {Nikolskiy}, Y. and 
	{Patrakeev}, A. and {Patsaev}, D. and {Santos-Skripko}, A. and 
	{Sazonov}, O. and {Semena}, N. and {Semenov}, A. and {Shashkin}, V. and 
	{Sidorov}, A. and {Stepanov}, A.~V. and {Stupin}, I. and {Timonin}, D. and 
	{Titov}, A.~Y. and {Viktorov}, A. and {Zharkov}, A. and {Altieri}, F. and 
	{Arnold}, G. and {Belyaev}, D.~A. and {Bertaux}, J.~L. and {Betsis}, D.~S. and 
	{Duxbury}, N. and {Encrenaz}, T. and {Fouchet}, T. and {Gérard}, J.-C. and 
	{Grassi}, D. and {Guerlet}, S. and {Hartogh}, P. and {Kasaba}, Y. and 
	{Khatuntsev}, I. and {Krasnopolsky}, V.~A. and {Kuzmin}, R.~O. and 
	{Lellouch}, E. and {Lopez-Valverde}, M.~A. and {Luginin}, M. and 
	{M{\"a}{\"a}tt{\"a}nen}, A. and {Marcq}, E. and {Martin Torres}, J. and 
	{Medvedev}, A.~S. and {Millour}, E. and {Olsen}, K.~S. and {Patel}, M.~R. and 
	{Quantin-Nataf}, C. and {Rodin}, A.~V. and {Shematovich}, V.~I. and 
	{Thomas}, I. and {Thomas}, N. and {Vazquez}, L. and {Vincendon}, M. and 
	{Wilquet}, V. and {Wilson}, C.~F. and {Zasova}, L.~V. and {Zelenyi}, L.~M. and 
	{Zorzano}, M.~P.},
  title = {{The Atmospheric Chemistry Suite (ACS) of Three Spectrometers for the ExoMars 2016 Trace Gas Orbiter}},
  journal = {\ssr},
  keywords = {Mars, Atmosphere, High-resolution spectrometer, Fourier-spectrometer, Echelle, Cross-dispersion},
  year = 2018,
  volume = 214,
  eid = {#7},
  pages = {#7},
  abstract = {{The Atmospheric Chemistry Suite (ACS) package is an element of the
Russian contribution to the ESA-Roscosmos ExoMars 2016 Trace Gas Orbiter
(TGO) mission. ACS consists of three separate infrared spectrometers,
sharing common mechanical, electrical, and thermal interfaces. This
ensemble of spectrometers has been designed and developed in response to
the Trace Gas Orbiter mission objectives that specifically address the
requirement of high sensitivity instruments to enable the unambiguous
detection of trace gases of potential geophysical or biological
interest. For this reason, ACS embarks a set of instruments achieving
simultaneously very high accuracy (ppt level), very high resolving power
($\gt$10,000) and large spectral coverage (0.7 to 17 {$\mu$}m{\mdash}the
visible to thermal infrared range). The near-infrared (NIR) channel is a
versatile spectrometer covering the 0.7-1.6 {$\mu$}m spectral range with a
resolving power of {\tilde}20,000. NIR employs the combination of an
echelle grating with an AOTF (Acousto-Optical Tunable Filter) as
diffraction order selector. This channel will be mainly operated in
solar occultation and nadir, and can also perform limb observations. The
scientific goals of NIR are the measurements of water vapor, aerosols,
and dayside or night side airglows. The mid-infrared (MIR) channel is a
cross-dispersion echelle instrument dedicated to solar occultation
measurements in the 2.2-4.4 {$\mu$}m range. MIR achieves a resolving power
of $\gt$50,000. It has been designed to accomplish the most sensitive
measurements ever of the trace gases present in the Martian atmosphere.
The thermal-infrared channel (TIRVIM) is a 2-inch double pendulum
Fourier-transform spectrometer encompassing the spectral range of 1.7-17
{$\mu$}m with apodized resolution varying from 0.2 to 1.3 cm$^{-1}$.
TIRVIM is primarily dedicated to profiling temperature from the surface
up to {\tilde}60 km and to monitor aerosol abundance in nadir. TIRVIM
also has a limb and solar occultation capability. The technical concept
of the instrument, its accommodation on the spacecraft, the optical
designs as well as some of the calibrations, and the expected
performances for its three channels are described.
  doi = {10.1007/s11214-017-0437-6},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Chaufray}, J.-Y. and {Gonzalez-Galindo}, F. and {Forget}, F. and 
	{Lopez-Valverde}, M. and {Leblanc}, F. and {Modolo}, R. and 
	{Hess}, S.},
  title = {{Reply to comment ``On the hydrogen escape: Comment to variability of the hydrogen in the Martian upper atmosphere as simulated by a 3D atmosphere-exosphere coupling by J.-Y. Chaufray et al.'' by V. Krasnopolsky, Icarus, 281, 262}},
  journal = {\icarus},
  year = 2018,
  volume = 301,
  pages = {132-135},
  abstract = {{Krasnopolsky (2017) makes a careful review of our recent results about
the Martian hydrogen content of the Martian upper atmosphere (Chaufray
et al., 2015). We comment here on his two major points. First, he
suggests that the non-thermal escape of H$_{2}$, and particularly
collisions with hot oxygen, not taken into account in our general
circulation model (GCM), should modify our reported H$_{2}$ and H
density profiles. This is an important issue; we acknowledge that future
effective coupling of our GCM with comprehensive models of the Martian
solar wind interaction, ideally after being validated with the latest
plasma observations of H$_{2}$$^{+}$, would allow for better
estimations of the relative importance of the H$_{2}$ non-thermal
and thermal escape processes. For the time being we need assumptions in
the GCM, with proper and regular updates. According to a recent and
detailed study of the anisotropic elastic and inelastic collision cross
sections between O and H$_{2}$ (Gacesa et al., 2012), the escape
rates used by Krasnopolsky (2010) for this process might be
overestimated. We therefore do not include non thermal escape of
H$_{2}$ in the model. And secondly, in response to Krasnopolsky's
comment on the H escape variability with the solar cycle, we revised our
calculations and found a small bug in the computation of the Jeans
effusion velocity. Our revised computed H escape rates are included
here. They have a small impact on our key conclusions: similar seasonal
variations, a reduced variation with the solar cycle but still larger
than Krasnopolsky (2017), and again a hydrogen scape systematically
lower than the diffusion-limited flux. This bug does not affect the
latest Mars Climate Database v5.2.
  doi = {10.1016/j.icarus.2017.07.013},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Erard}, S. and {Cecconi}, B. and {Le Sidaner}, P. and {Rossi}, A.~P. and 
	{Capria}, M.~T. and {Schmitt}, B. and {Génot}, V. and {André}, N. and 
	{Vandaele}, A.~C. and {Scherf}, M. and {Hueso}, R. and {M{\"a}{\"a}tt{\"a}nen}, A. and 
	{Thuillot}, W. and {Carry}, B. and {Achilleos}, N. and {Marmo}, C. and 
	{Santolik}, O. and {Benson}, K. and {Fernique}, P. and {Beigbeder}, L. and 
	{Millour}, E. and {Rousseau}, B. and {Andrieu}, F. and {Chauvin}, C. and 
	{Minin}, M. and {Ivanoski}, S. and {Longobardo}, A. and {Bollard}, P. and 
	{Albert}, D. and {Gangloff}, M. and {Jourdane}, N. and {Bouchemit}, M. and 
	{Glorian}, J.-M. and {Trompet}, L. and {Al-Ubaidi}, T. and {Juaristi}, J. and 
	{Desmars}, J. and {Guio}, P. and {Delaa}, O. and {Lagain}, A. and 
	{Soucek}, J. and {Pisa}, D.},
  title = {{VESPA: A community-driven Virtual Observatory in Planetary Science}},
  journal = {\planss},
  archiveprefix = {arXiv},
  eprint = {1705.09727},
  primaryclass = {astro-ph.IM},
  keywords = {Virtual Observatory, Solar System, GIS},
  year = 2018,
  volume = 150,
  pages = {65-85},
  abstract = {{The VESPA data access system focuses on applying Virtual Observatory
(VO) standards and tools to Planetary Science. Building on a previous
EC-funded Europlanet program, it has reached maturity during the first
year of a new Europlanet 2020 program (started in 2015 for 4 years). The
infrastructure has been upgraded to handle many fields of Solar System
studies, with a focus both on users and data providers. This paper
describes the broad lines of the current VESPA infrastructure as seen by
a potential user, and provides examples of real use cases in several
thematic areas. These use cases are also intended to identify hints for
future developments and adaptations of VO tools to Planetary Science.
  doi = {10.1016/j.pss.2017.05.013},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Guerlet}, S. and {Fouchet}, T. and {Spiga}, A. and {Flasar}, F.~M. and 
	{Fletcher}, L.~N. and {Hesman}, B.~E. and {Gorius}, N.},
  title = {{Equatorial Oscillation and Planetary Wave Activity in Saturn's Stratosphere Through the Cassini Epoch}},
  journal = {Journal of Geophysical Research (Planets)},
  keywords = {Saturn, Cassini, atmosphere, infrared remote sensing, stratospheric dynamics},
  year = 2018,
  volume = 123,
  pages = {246-261},
  abstract = {{Thermal infrared spectra acquired by Cassini/Composite InfraRed
Spectrometer (CIRS) in limb-viewing geometry in 2015 are used to derive
2-D latitude-pressure temperature and thermal wind maps. These maps are
used to study the vertical structure and evolution of Saturn's
equatorial oscillation (SEO), a dynamical phenomenon presenting
similarities with the Earth's quasi-biennal oscillation (QBO) and
semi-annual oscillation (SAO). We report that a new local wind maximum
has appeared in 2015 in the upper stratosphere and derive the descent
rates of other wind extrema through time. The phase of the oscillation
observed in 2015, as compared to 2005 and 2010, remains consistent with
a {\tilde}15 year period. The SEO does not propagate downward at a
regular rate but exhibits faster descent rate in the upper stratosphere,
combined with a greater vertical wind shear, compared to the lower
stratosphere. Within the framework of a QBO-type oscillation, we
estimate the absorbed wave momentum flux in the stratosphere to be on
the order of {\tilde}7 {\times} 10$^{-6}$ N m$^{-2}$. On
Earth, interactions between vertically propagating waves (both planetary
and mesoscale) and the mean zonal flow drive the QBO and SAO. To broaden
our knowledge on waves potentially driving Saturn's equatorial
oscillation, we searched for thermal signatures of planetary waves in
the tropical stratosphere using CIRS nadir spectra. Temperature
anomalies of amplitude 1-4 K and zonal wave numbers 1 to 9 are
frequently observed, and an equatorial Rossby (n = 1) wave of zonal wave
number 3 is tentatively identified in November 2009.
  doi = {10.1002/2017JE005419},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Moore}, J.~M. and {Howard}, A.~D. and {Umurhan}, O.~M. and 
	{White}, O.~L. and {Schenk}, P.~M. and {Beyer}, R.~A. and {McKinnon}, W.~B. and 
	{Spencer}, J.~R. and {Singer}, K.~N. and {Grundy}, W.~M. and 
	{Earle}, A.~M. and {Schmitt}, B. and {Protopapa}, S. and {Nimmo}, F. and 
	{Cruikshank}, D.~P. and {Hinson}, D.~P. and {Young}, L.~A. and 
	{Stern}, S.~A. and {Weaver}, H.~A. and {Olkin}, C.~B. and {Ennico}, K. and 
	{Collins}, G. and {Bertrand}, T. and {Forget}, F. and {Scipioni}, F. and 
	{New Horizons Science Team}},
  title = {{Bladed Terrain on Pluto: Possible origins and evolution}},
  journal = {\icarus},
  keywords = {Pluto, Atmosphere, Ices, Mechanical properties, Geological processes, IR spectroscopy, Surface},
  year = 2018,
  volume = 300,
  pages = {129-144},
  abstract = {{Bladed Terrain on Pluto consists of deposits of massive CH$_{4}$,
which are observed to occur within latitudes 30{\deg} of the equator and
are found almost exclusively at the highest elevations ($\gt$ 2 km above
the mean radius). Our analysis indicates that these deposits of
CH$_{4}$ preferentially precipitate at low latitudes where net
annual solar energy input is lowest. CH$_{4}$ and N$_{2}$
will both precipitate at low elevations. However, since there is much
more N$_{2}$ in the atmosphere than CH$_{4}$, the
N$_{2}$ ice will dominate at these low elevations. At high
elevations the atmosphere is too warm for N$_{2}$ to precipitate
so only CH$_{4}$ can do so. We conclude that following the time of
massive CH$_{4}$ emplacement; there have been sufficient
excursions in Pluto's climate to partially erode these deposits via
sublimation into the blades we see today. Blades composed of massive
CH$_{4}$ ice implies that the mechanical behavior of
CH$_{4}$ can support at least several hundred meters of relief at
Pluto surface conditions. Bladed Terrain deposits may be widespread in
the low latitudes of the poorly seen sub-Charon hemisphere, based on
spectral observations. If these locations are indeed Bladed Terrain
deposits, they may mark heretofore unrecognized regions of high
  doi = {10.1016/j.icarus.2017.08.031},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  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 = {}, adsnote = {Provided by the SAO/NASA Astrophysics Data System} }