pub2017.bib
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@article{2017SSRv..212.1541S,
author = {{S{\'a}nchez-Lavega}, A. and {Lebonnois}, S. and {Imamura}, T. and
{Read}, P. and {Luz}, D.},
title = {{The Atmospheric Dynamics of Venus}},
journal = {\ssr},
keywords = {Venus, Atmospheric dynamics},
year = 2017,
volume = 212,
pages = {1541-1616},
abstract = {{We review our current knowledge of the atmospheric dynamics of Venus
prior to the Akatsuki mission, in the altitude range from the surface to
approximately the cloud tops located at about 100 km altitude. The
three-dimensional structure of the wind field in this region has been
determined with a variety of techniques over a broad range of spatial
and temporal scales (from the mesoscale to planetary, from days to
years, in daytime and nighttime), spanning a period of about 50 years
(from the 1960s to the present). The global panorama is that the mean
atmospheric motions are essentially zonal, dominated by the so-called
super-rotation (an atmospheric rotation that is 60 to 80 times faster
than that of the planetary body). The zonal winds blow westward (in the
same direction as the planet rotation) with a nearly constant speed of
{\tilde} 100 m s\^{}$\{$-1$\}$ at the cloud tops (65-70 km altitude) from latitude
50{\deg}N to 50{\deg}S, then decreasing their speeds monotonically from
these latitudes toward the poles. Vertically, the zonal winds decrease
with decreasing altitude towards velocities {\tilde} 1-3 m s\^{}$\{$-1$\}$ in a
layer of thickness {\tilde} 10 km close to the surface. Meridional
motions with peak speeds of {\tilde} 15 m s\^{}$\{$-1$\}$ occur within the upper
cloud at 65 km altitude and are related to a Hadley cell circulation and
to the solar thermal tide. Vertical motions with speeds {\tilde}1-3 m
s\^{}$\{$-1$\}$ occur in the statically unstable layer between altitudes of
{\tilde} 50 - 55 km. All these motions are permanent with speed
variations of the order of {\tilde}10\%. Various types of wave, from
mesoscale gravity waves to Rossby-Kelvin planetary scale waves, have
been detected at and above cloud heights, and are considered to be
candidates as agents for carrying momentum that drives the
super-rotation, although numerical models do not fully reproduce all the
observed features. Momentum transport by atmospheric waves and the solar
tide is thought to be an indispensable component of the general
circulation of the Venus atmosphere. Another conspicuous feature of the
atmospheric circulation is the presence of polar vortices. These are
present in both hemispheres and are regions of warmer and lower clouds,
seen prominently at infrared wavelengths, showing a highly variable
morphology and motions. The vortices spin with a period of 2-3 days. The
South polar vortex rotates around a geographical point which is itself
displaced from the true pole of rotation by {\tilde} 3 degrees. The polar
vortex is surrounded and constrained by the cold collar, an
infrared-dark region of lower temperatures. We still lack detailed
models of the mechanisms underlying the dynamics of these features and
how they couple (or not) to the super-rotation. The nature of the
super-rotation relates to the angular momentum stored in the atmosphere
and how it is transported between the tropics and higher latitudes, and
between the deep atmosphere and upper levels. The role of eddy processes
is crucial, but likely involves the complex interaction of a variety of
different types of eddy, either forced directly by radiative heating and
mechanical interactions with the surface or through various forms of
instability. Numerical models have achieved some significant recent
success in capturing some aspects of the observed super-rotation,
consistent with the scenario discussed by Gierasch (J. Atmos. Sci.
32:1038-1044, 1975) and Rossow and Williams (J. Atmos. Sci. 36:377-389,
1979), but many uncertainties remain, especially in the deep atmosphere.
The theoretical framework developed to explain the circulation in
Venus's atmosphere is reviewed, as well as the numerical models that
have been built to elucidate the super-rotation mechanism. These tools
are used to analyze the respective roles of the different waves in the
processes driving the observed motions. Their limitations and suggested
directions for improvements are discussed.
}},
doi = {10.1007/s11214-017-0389-x},
adsurl = {https://ui.adsabs.harvard.edu/abs/2017SSRv..212.1541S},
localpdf = {REF/2017SSRv..212.1541S.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2017Icar..294..124L,
author = {{Limaye}, S.~S. and {Lebonnois}, S. and {Mahieux}, A. and {P{\"a}tzold}, M. and
{Bougher}, S. and {Bruinsma}, S. and {Chamberlain}, S. and {Clancy}, R.~T. and
{Gérard}, J.-C. and {Gilli}, G. and {Grassi}, D. and {Haus}, R. and
{Herrmann}, M. and {Imamura}, T. and {Kohler}, E. and {Krause}, P. and
{Migliorini}, A. and {Montmessin}, F. and {Pere}, C. and {Persson}, M. and
{Piccialli}, A. and {Rengel}, M. and {Rodin}, A. and {Sandor}, B. and
{Sornig}, M. and {Svedhem}, H. and {Tellmann}, S. and {Tanga}, P. and
{Vandaele}, A.~C. and {Widemann}, T. and {Wilson}, C.~F. and
{M{\"u}ller-Wodarg}, I. and {Zasova}, L.},
title = {{The thermal structure of the Venus atmosphere: Intercomparison of Venus Express and ground based observations of vertical temperature and density profiles$^{✰}$}},
journal = {\icarus},
year = 2017,
volume = 294,
pages = {124-155},
abstract = {{The Venus International Reference Atmosphere (VIRA) model contains
tabulated values of temperature and number densities obtained by the
experiments on the Venera entry probes, Pioneer Venus Orbiter and
multi-probe missions in the 1980s. The instruments on the recent Venus
Express orbiter mission generated a significant amount of new
observational data on the vertical and horizontal structure of the Venus
atmosphere from 40 km to about 180 km altitude from April 2006 to
November 2014. Many ground based experiments have provided data on the
upper atmosphere (90-130 km) temperature structure since the publication
of VIRA in 1985. The ``Thermal Structure of the Venus Atmosphere'' Team
was supported by the International Space Studies Institute (ISSI), Bern,
Switzerland, from 2013 to 2015 in order to combine and compare the
ground-based observations and the VEx observations of the thermal
structure as a first step towards generating an updated VIRA model.
Results of this comparison are presented in five latitude bins and three
local time bins by assuming hemispheric symmetry. The intercomparison of
the ground-based and VEx results provides for the first time a
consistent picture of the temperature and density structure in the 40
km-180 km altitude range. The Venus Express observations have
considerably increased our knowledge of the Venus atmospheric thermal
structure above {\sim}40 km and provided new information above 100 km.
There are, however, still observational gaps in latitude and local time
above certain regions. Considerable variability in the temperatures and
densities is seen above 100 km but certain features appear to be
systematically present, such as a succession of warm and cool layers.
Preliminary modeling studies support the existence of such layers in
agreement with a global scale circulation. The intercomparison focuses
on average profiles but some VEx experiments provide sufficient global
coverage to identify solar thermal tidal components.
The differences between the VEx temperature profiles and the VIRA below
0.1 mbar/95 km are small. There is, however, a clear discrepancy at high
latitudes in the 10-30 mbar (70-80 km) range. The VEx observations will
also allow the improvement of the empirical models (VTS3 by Hedin et
al., 1983 and VIRA by Keating et al., 1985) above 0.03 mbar/100 km, in
particular the 100-150 km region where a sufficient observational
coverage was previously missing. The next steps in order to define the
updated VIRA temperature structure up to 150 km altitude are (1) define
the grid on which this database may be provided, (2) fill what is
possible with the results of the data intercomparison, and (3) fill the
observational gaps. An interpolation between the datasets may be
performed by using available General Circulation Models as guidelines.
An improved spatial coverage of observations is still necessary at all
altitudes, in latitude-longitude and at all local solar times for a
complete description of the atmospheric thermal structure, in particular
on the dayside above 100 km. New in-situ observations in the atmosphere
below 40 km are missing, an altitude region that cannot be accessed by
occultation experiments. All these questions need to be addressed by
future missions.
}},
doi = {10.1016/j.icarus.2017.04.020},
adsurl = {https://ui.adsabs.harvard.edu/abs/2017Icar..294..124L},
localpdf = {REF/2017Icar..294..124L.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2017NatGe..10..473L,
author = {{Lebonnois}, S. and {Schubert}, G.},
title = {{The deep atmosphere of Venus and the possible role of density-driven separation of CO$_{2}$ and N$_{2}$}},
journal = {Nature Geoscience},
year = 2017,
volume = 10,
pages = {473-477},
abstract = {{With temperatures around 700 K and pressures of around 75 bar, the
deepest 12 km of the atmosphere of Venus are so hot and dense that the
atmosphere behaves like a supercritical fluid. The Soviet VeGa-2 probe
descended through the atmosphere in 1985 and obtained the only reliable
temperature profile for the deep Venusian atmosphere thus far. In this
temperature profile, the atmosphere appears to be highly unstable at
altitudes below 7 km, contrary to expectations. We argue that the VeGa-2
temperature profile could be explained by a change in the atmospheric
gas composition, and thus molecular mass, with depth. We propose that
the deep atmosphere consists of a non-homogeneous layer in which the
abundance of N$_{2}$--the second most abundant constituent of the
Venusian atmosphere after CO$_{2}$--gradually decreases to
near-zero at the surface. It is difficult to explain a decline in
N$_{2}$ towards the surface with known nitrogen sources and sinks
for Venus. Instead we suggest, partly based on experiments on
supercritical fluids, that density-driven separation of N$_{2}$
from CO$_{2}$ can occur under the high pressures of Venus's deep
atmosphere, possibly by molecular diffusion, or by natural
density-driven convection. If so, the amount of nitrogen in the
atmosphere of Venus is 15\% lower than commonly assumed. We suggest that
similar density-driven separation could occur in other massive planetary
atmospheres.
}},
doi = {10.1038/ngeo2971},
adsurl = {https://ui.adsabs.harvard.edu/abs/2017NatGe..10..473L},
localpdf = {REF/2017NatGe..10..473L.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2017JGRE..122..134L,
author = {{Lef{\`e}vre}, M. and {Spiga}, A. and {Lebonnois}, S.},
title = {{Three-dimensional turbulence-resolving modeling of the Venusian cloud layer and induced gravity waves}},
journal = {Journal of Geophysical Research (Planets)},
keywords = {3-D mesoscale modeling, Venus, convective cloud layer, gravity waves},
year = 2017,
volume = 122,
pages = {134-149},
abstract = {{The impact of the cloud convective layer of the atmosphere of Venus on
the global circulation remains unclear. The recent observations of
gravity waves at the top of the cloud by the Venus Express mission
provided some answers. These waves are not resolved at the scale of
global circulation models (GCM); therefore, we developed an
unprecedented 3-D turbulence-resolving large-eddy simulations (LES)
Venusian model using the Weather Research and Forecast terrestrial
model. The forcing consists of three different heating rates: two
radiative ones for solar and infrared and one associated with the
adiabatic cooling/warming of the global circulation. The rates are
extracted from the Laboratoire de Météorlogie Dynamique
Venus GCM using two different cloud models. Thus, we are able to
characterize the convection and associated gravity waves in function of
latitude and local time. To assess the impact of the global circulation
on the convective layer, we used rates from a 1-D radiative-convective
model. The resolved layer, taking place between 1.0 {\times}
10$^{5}$ and 3.8 {\times} 10$^{4}$ Pa (48-53 km), is
organized as polygonal closed cells of about 10 km wide with vertical
wind of several meters per second. The convection emits gravity waves
both above and below the convective layer leading to temperature
perturbations of several tenths of kelvin with vertical wavelength
between 1 and 3 km and horizontal wavelength from 1 to 10 km. The
thickness of the convective layer and the amplitudes of waves are
consistent with observations, though slightly underestimated. The global
dynamics heating greatly modify the convective layer.
}},
doi = {10.1002/2016JE005146},
adsurl = {https://ui.adsabs.harvard.edu/abs/2017JGRE..122..134L},
localpdf = {REF/2017JGRE..122..134L.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2017Icar..281...55G,
author = {{Gilli}, G. and {Lebonnois}, S. and {Gonz{\'a}lez-Galindo}, F. and
{L{\'o}pez-Valverde}, M.~A. and {Stolzenbach}, A. and {Lefèvre}, F. and
{Chaufray}, J.~Y. and {Lott}, F.},
title = {{Thermal structure of the upper atmosphere of Venus simulated by a ground-to-thermosphere GCM}},
journal = {\icarus},
year = 2017,
volume = 281,
pages = {55-72},
abstract = {{We present here the thermal structure of the upper atmosphere of Venus
predicted by a full self-consistent Venus General Circulation Model
(VGCM) developed at Laboratoire de Météorologie Dynamique
(LMD) and extended up to the thermosphere of the planet. Physical and
photochemical processes relevant at those altitudes, plus a
non-orographic GW parameterisation, have been added. All those
improvements make the LMD-VGCM the only existing ground-to-thermosphere
3D model for Venus: a unique tool to investigate the atmosphere of Venus
and to support the exploration of the planet by remote sounding. The aim
of this paper is to present the model reference results, to describe the
role of radiative, photochemical and dynamical effects in the observed
thermal structure in the upper mesosphere/lower thermosphere of the
planet. The predicted thermal structure shows a succession of warm and
cold layers, as recently observed. A cooling trend with increasing
latitudes is found during daytime at all altitudes, while at nighttime
the trend is inverse above about 110 km, with an atmosphere up to 15 K
warmer towards the pole. The latitudinal variation is even smaller at
the terminator, in agreement with observations. Below about 110 km, a
nighttime warm layer whose intensity decreases with increasing latitudes
is predicted by our GCM. A comparison of model results with a selection
of recent measurements shows an overall good agreement in terms of
trends and order of magnitude. Significant data-model discrepancies may
be also discerned. Among them, thermospheric temperatures are about
40-50 K colder and up to 30 K warmer than measured at terminator and at
nighttime, respectively. The altitude layer of the predicted mesospheric
local maximum (between 100 and 120 km) is also higher than observed.
Possible interpretations are discussed and several sensitivity tests
performed to understand the data-model discrepancies and to propose
future model improvements.
}},
doi = {10.1016/j.icarus.2016.09.016},
adsurl = {https://ui.adsabs.harvard.edu/abs/2017Icar..281...55G},
localpdf = {REF/2017Icar..281...55G.pdf},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}