pub2021.bib
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@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{2021Icar..36614432G,
author = {{Gilli}, G. and {Navarro}, T. and {Lebonnois}, S. and {Quirino}, D. and {Silva}, V. and {Stolzenbach}, A. and {Lef{\`e}vre}, F. and {Schubert}, G.},
title = {{Venus upper atmosphere revealed by a GCM: II. Model validation with temperature and density measurements}},
journal = {\icarus},
keywords = {Venus GCM, Upper atmosphere, Variability, Transition region, Astrophysics - Earth and Planetary Astrophysics, Physics - Atmospheric and Oceanic Physics},
year = 2021,
month = sep,
volume = {366},
eid = {114432},
pages = {114432},
abstract = {{An improved high resolution (96 longitude by 96 latitude points) ground-
to-thermosphere version of the Institut Pierre-Simon Laplace
(IPSL) Venus General Circulation Model (VGCM), including non-
orographic gravity waves (GW) parameterization and fine-tuned
non-LTE parameters, is presented here. We focus on the
validation of the model built from a collection of data mostly
from Venus Express (2006-2014) experiments and coordinated
ground-based telescope campaigns, in the upper mesosphere/lower
thermosphere of Venus (80-150 km). These simulations result in
an overall better agreement with temperature observations above
90 km, compared with previous versions of the VGCM. Density of
CO$_{2}$ and light species, such as CO and O, are also
comparable with observations in terms of trend and order of
magnitude. Systematic biases in the temperature structure are
found between 80 and 100 km approximately (e.g. GCM is 20 to 40
K warmer than measurements) and above 130 km at the terminator
(e.g. GCM is up to 50 K colder than observed). Possible
candidates for those discrepancies are the uncertainties on the
collisional rate coefficients used in the non-LTE
parameterization (above 130 km), and assumptions on the CO$_{2}$
mixing ratio made for stellar/solar occultation retrievals.
Diurnal and latitudinal distribution of dynamical tracers (i.e.
CO and O) are also analyzed, in a region poorly constrained by
wind measurements and characterized by high variability over
daily to weekly timescale. Overall, our simulations indicate
that a weak westward retrograde wind is present in the
mesosphere, up to about 120 km, producing the CO bulge
displacement toward 2 h-3 h in the morning, instead of piling up
at the anti-solar point, as for an idealized sub-solar to anti-
solar circulation. This retrograde imbalance is suggested to be
produced by perturbations of a \raisebox{-0.5ex}\textasciitilde
5 days Kelvin wave impacting the mesosphere up to 110 km
(described in a companion paper Navarro et al., 2021), combined
with GW westward acceleration in the lower thermosphere, mostly
above 110 km. On the whole, these model developments point to
the importance of the inclusion of the lower atmosphere, higher
resolution and finely tuned parameterizations in GCM of the
Venusian upper atmosphere, in order to shed light on existing
observations.}},
doi = {10.1016/j.icarus.2021.114432},
archiveprefix = {arXiv},
eprint = {2103.15649},
primaryclass = {astro-ph.EP},
localpdf = {REF/2021Icar..36614432G.pdf},
adsurl = {https://ui.adsabs.harvard.edu/abs/2021Icar..36614432G},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2021Icar..36614400N,
author = {{Navarro}, T. and {Gilli}, G. and {Schubert}, G. and {Lebonnois}, S. and {Lef{\`e}vre}, F. and {Quirino}, D.},
title = {{Venus' upper atmosphere revealed by a GCM: I. Structure and variability of the circulation}},
journal = {\icarus},
keywords = {Venus, GCM, Upper atmosphere, Atmospheric circulation, Airglow, Kelvin wave, Singlet oxygen},
year = 2021,
month = sep,
volume = {366},
eid = {114400},
pages = {114400},
abstract = {{A numerical simulation of the upper atmosphere of Venus is carried out
with an improved version of the Institut Pierre-Simon Laplace
(IPSL) full-physics Venus General Circulation Model (GCM). This
simulation reveals the organization of the atmospheric
circulation at an altitude above 80 km in unprecedented detail.
Converging flow towards the antisolar point results in
supersonic wind speeds and generates a shock-like feature past
the terminator at altitudes above 110 km. This shock-like
feature greatly decreases nightside thermospheric wind speeds,
favoring atmospheric variability on a hourly timescale in the
nightside of the thermosphere. A {\ensuremath{\sim}}5-day period
Kelvin wave originating in the cloud deck is found to
substantially impact the Venusian upper atmosphere circulation.
As the Kelvin wave impacts the nightside, the poleward
meridional circulation is enhanced. Consequently, recombined
molecular oxygen is periodically ejected to high latitudes,
explaining the characteristics of the various observations of
oxygen nightglow at 1 . 27 {\ensuremath{\mu}}m . An analysis of
the simulated 1 . 27 {\ensuremath{\mu}}m oxygen nightglow shows
that it is not necessarily a good tracer of the upper
atmospheric dynamics, since contributions from chemical
processes and vertical transport often prevail over horizontal
transport. Moreover, dayside atomic oxygen abundances also vary
periodically as the Kelvin wave momentarily decreases horizontal
wind speeds and enhances atomic oxygen abundances, explaining
the observations of EUV oxygen dayglow. Despite the nitrogen
chemistry not being currently included in the IPSL Venus GCM,
the apparent maximum NO nightglow shifted towards the morning
terminator might be explained by the simulated structure of
winds.}},
doi = {10.1016/j.icarus.2021.114400},
localpdf = {REF/2021Icar..36614400N.pdf},
adsurl = {https://ui.adsabs.harvard.edu/abs/2021Icar..36614400N},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2021A&A...649A..34S,
author = {{Silva}, J.~E. and {Machado}, P. and {Peralta}, J. and {Brasil}, F. and {Lebonnois}, S. and {Lef{\`e}vre}, M.},
title = {{Characterising atmospheric gravity waves on the nightside lower clouds of Venus: a systematic analysis}},
journal = {\aap},
keywords = {waves, planets and satellites: atmospheres, planets and satellites: terrestrial planets, methods: observational, planets and satellites: individual: atmosphere dynamics: cloud tracking, planets and satellites: individual: Venus, Astrophysics - Earth and Planetary Astrophysics},
year = 2021,
month = may,
volume = {649},
eid = {A34},
pages = {A34},
abstract = {{We present the detection and characterisation of mesoscale waves on the
lower clouds of Venus using images from the Visible Infrared
Thermal Imaging Spectrometer onboard the European Venus Express
space mission and from the 2 {\ensuremath{\mu}}m camera (IR2)
instrument onboard the Japanese space mission Akatsuki. We used
image navigation and processing techniques based on contrast
enhancement and geometrical projections to characterise
morphological properties of the detected waves, such as
horizontal wavelength and the relative optical thickness drop
between crests and troughs. Additionally, we performed phase
velocity and trajectory tracking of wave packets. We combined
these observations to derive other properties of the waves such
as the vertical wavelength of detected packets. Our observations
include 13 months of data from August 2007 to October 2008, and
the entire available data set of IR2 from January to November
2016. We characterised almost 300 wave packets across more than
5500 images over a broad region of the globe of Venus. Our
results show a wide range of properties and are not only
consistent with previous observations but also expand upon them,
taking advantage of two instruments that target the same cloud
layer of Venus across multiple periods. In general, waves
observed on the nightside lower cloud are of a larger scale than
the gravity waves reported in the upper cloud. This paper is
intended to provide a more in-depth view of atmospheric gravity
waves on the lower cloud and enable follow-up works on their
influence in the general circulation of Venus.}},
doi = {10.1051/0004-6361/202040193},
archiveprefix = {arXiv},
eprint = {2105.04931},
primaryclass = {astro-ph.EP},
localpdf = {REF/2021A&A...649A..34S.pdf},
adsurl = {https://ui.adsabs.harvard.edu/abs/2021A&A...649A..34S},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}