@comment{{This file has been generated by bib2bib 1.94}}
@comment{{Command line: /usr/bin/bib2bib --quiet -c 'not journal:"Discussions"' -c year=2008 -c $type="ARTICLE" -oc pub2008.txt -ob pub2008.bib}}
  author = {{Gonz{\'a}lez-Galindo}, F. and {Forget}, F. and {Angelats I Coll}, M. and 
	{L{\'o}pez-Valverde}, M.~A.},
  title = {{The Martian upper atmosphere}},
  journal = {Lecture Notes and Essays in Astrophysics},
  keywords = {Mars atmosphere, Thermosphere, General Circulation Models},
  year = 2008,
  volume = 3,
  pages = {151-162},
  abstract = {{The most relevant aspects of the Martian atmosphere are presented in
this paper, focusing on the almost unexplored upper atmosphere. We
summarize the most recent observations concerning this region, as well
as the numerical models used to its study. Special attention is devoted
to the only ground-to-exosphere General Circulation Model existing today
for Mars, the LMD-MGCM. The model and its extension to the thermosphere
are described and the strategies used for its validation are shortly
discussed. Finally, we briefly present some comparisons between the
results of the model and the observations by different spacecrafts.
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  author = {{Fastook}, J.~L. and {Head}, J.~W. and {Marchant}, D.~R. and 
	{Forget}, F.},
  title = {{Tropical mountain glaciers on Mars: Altitude-dependence of ice accumulation, accumulation conditions, formation times, glacier dynamics, and implications for planetary spin-axis/orbital history}},
  journal = {\icarus},
  year = 2008,
  volume = 198,
  pages = {305-317},
  abstract = {{Fan-shaped deposits up to {\tilde}166,000 km in area are found on the
northwest flanks of the huge Tharsis Montes volcanoes in the tropics of
Mars. Recent spacecraft data have confirmed earlier hypotheses that
these lobate deposits are glacial in origin. Increased knowledge of
polar-latitude terrestrial glacial analogs in the Antarctic Dry Valleys
has been used to show that the lobate deposits are the remnants of
cold-based glaciers that formed in the extremely cold, hyper-arid
climate of Mars. Mars atmospheric general circulation models (GCM) show
that these glaciers could form during periods of high obliquity when
upwelling and adiabatic cooling of moist air favor deposition of snow on
the northwest flanks of the Tharsis Montes. We present a simulation of
the Tharsis Montes ice sheets produced by a static accumulation pattern
based on the GCM results and compare this with the nature and extent of
the geologic deposits. We use the fundamental differences between the
atmospheric snow accumulation environments (mass balance) on Earth and
Mars, geological observations and ice-sheet models to show that two
equilibrium lines should characterize ice-sheet mass balance on Mars,
and that glacial accumulation should be favored on the flanks of large
volcanoes, not on their summits as seen on Earth. Predicted accumulation
rates from such a parameterization, together with sample spin-axis
obliquity histories, are used to show that obliquity in excess of
45{\deg} and multiple 120,000 year obliquity cycles are necessary to
produce the observed deposits. Our results indicate that the formation
of these deposits required multiple successive stages of advance and
retreat before their full extent could be reached, and thus imply that
spin-axis obliquity remained at these high values for millions of years
during the Late Amazonian period of Mars history. Spin-axis obliquity is
one of the main factors in the distribution and intensity of solar
insolation, and thus in determining the climate history of Mars.
Unfortunately, reconstruction of past climate history is inhibited by
the fact that the chaotic nature of the solution makes the calculation
of orbital histories unreliable prior to about 20 Ma ago. We show,
however, that the geological record, combined with glacial modeling, can
be used to provide insight into the nature of the spin-axis/orbital
history of Mars in the Late Amazonian, and to begin to establish data
points for the geologically based reconstruction of the climate and
orbital history of Mars.
  doi = {10.1016/j.icarus.2008.08.008},
  adsurl = {},
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  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 [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
  doi = {10.1016/j.icarus.2008.05.010},
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  author = {{Giuranna}, M. and {Grassi}, D. and {Formisano}, V. and {Montabone}, L. and 
	{Forget}, F. and {Zasova}, L.},
  title = {{PFS/MEX observations of the condensing CO $_{2}$ south polar cap of Mars}},
  journal = {\icarus},
  year = 2008,
  volume = 197,
  pages = {386-402},
  abstract = {{The condensing CO $_{2}$ south polar cap of Mars and the
mechanisms of the CO $_{2}$ ice accumulation have been studied
through the analysis of spectra acquired by the Planetary Fourier
Spectrometer (PFS) during the first two years of ESA's Mars Express
(MEX) mission. This dataset spans more than half a martian year, from
Ls{\tilde}330{\deg} to Ls{\tilde}194{\deg}, and includes the southern fall
season which is found to be extremely important for the study of the
residual south polar cap asymmetry. The cap expands symmetrically and
with constant speed during the fall season. The maximum extension occurs
sometime in the 80{\deg}-90{\deg} Ls range, when the cap edges are as low
as -40{\deg} latitude. Inside Hellas and Argyre basins, frost can be
stable at lower latitudes due to the higher pressure values, causing the
seasonal cap to be asymmetric. Within the seasonal range considered in
this paper, the cap edge recession rate is approximately half the rate
at which the cap edge expanded. The longitudinal asymmetries reduce
during the cap retreat, and disappear around Ls{\tilde}145{\deg}. Two
different mechanisms are responsible for CO $_{2}$ ice
accumulation during the fall season, especially in the 50{\deg}-70{\deg}
Ls range. Here, CO $_{2}$ condensation in the atmosphere, and thus
precipitation, is allowed exclusively in the western hemisphere, and
particularly in the longitudinal corridor of the perennial cap. In the
eastern hemisphere, the cap consists mainly of CO $_{2}$ frost
deposits, as a consequence of direct vapor deposition. The differences
in the nature of the surface ice deposits are the main cause for the
residual south polar cap asymmetry. Results from selected PFS orbits
have also been compared with the results provided by the martian general
circulation model (GCM) of the Laboratoire de Météorologie
dynamique (LMD) in Paris, with the aim of putting the observations in
the context of the global circulation. This first attempt of
cross-validation between PFS measurements and the LMD GCM on the one
hand confirms the interpretation of the observations, and on the other
hand shows that the climate modeling during the southern polar night on
Mars is extremely sensitive to the dynamical forcing.
  doi = {10.1016/j.icarus.2008.05.019},
  adsurl = {},
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  author = {{Cavalié}, T. and {Billebaud}, F. and {Encrenaz}, T. and 
	{Dobrijevic}, M. and {Brillet}, J. and {Forget}, F. and {Lellouch}, E.
  title = {{Vertical temperature profile and mesospheric winds retrieval on Mars from CO ;millimeter observations. Comparison with general circulation model predictions}},
  journal = {\aap},
  keywords = {planets and satellites: individual: Mars, radio lines: solar system},
  year = 2008,
  volume = 489,
  pages = {795-809},
  abstract = {{Aims: We have recorded high spectral resolution spectra and derived
precise atmospheric temperature profiles and wind velocities in the
atmosphere of Mars. We have compared observations of the planetary mean
thermal profile and mesospheric wind velocities on the disk, obtained
with our millimetric observations of CO rotational lines, to predictions
from the Laboratoire de Météorologie Dynamique (LMD) Mars
General Circulation Model, as provided through the Mars Climate Database
(MCD) numerical tool.  
Methods: We observed the atmosphere of Mars at CO(1-0) and CO(2-1) wavelengths with the IRAM 30-m antenna in June 2001 and November 2005. We retrieved the mean thermal profile of the planet from high and low spectral resolution data with an inversion method detailed here. High spectral resolution spectra were used to derive mesospheric wind velocities on the planetary disk. We also report here the use of $^{13}$CO(2-1) line core shifts to measure wind velocities at 40 km.
Results: Neither the Mars Year 24 (MY24) nor the Dust Storm scenario from the Mars Climate Database (MCD) provides satisfactory fits to the 2001 and 2005 data when retrieving the thermal profiles. The Warm scenario only provides good fits for altitudes lower than 30 km. The atmosphere is warmer than predicted up to 60 km and then becomes colder. Dust loading could be the reason for this mismatch. The MCD MY24 scenario predicts a thermal inversion layer between 40 and 60 km, which is not retrieved from the high spectral resolution data. Our results are generally in agreement with other observations from 10 to 40 km in altitude, but our results obtained from the high spectral resolution spectra differ in the 40-70 km layer, where the instruments are the most sensitive. The wind velocities we retrieve from our $^{12}$CO observations confirm MCD predictions for 2001 and 2005. Velocities obtained from $^{13}$CO observations are consistent with MCD predictions in 2001, but are lower than predicted in 2005. }}, doi = {10.1051/0004-6361:200809815}, adsurl = {}, adsnote = {Provided by the SAO/NASA Astrophysics Data System} }
  author = {{Wilson}, C.~F. and {Guerlet}, S. and {Irwin}, P.~G.~J. and 
	{Tsang}, C.~C.~C. and {Taylor}, F.~W. and {Carlson}, R.~W. and 
	{Drossart}, P. and {Piccioni}, G.},
  title = {{Evidence for anomalous cloud particles at the poles of Venus}},
  journal = {Journal of Geophysical Research (Planets)},
  keywords = {Planetary Sciences: Solar System Objects: Venus, Planetary Sciences: Comets and Small Bodies: Atmospheres (1060), Planetary Sciences: Comets and Small Bodies: Radiation and chemistry, Atmospheric Composition and Structure: Planetary atmospheres (5210, 5405, 5704), Atmospheric Composition and Structure: Aerosols and particles (0345, 4801, 4906)},
  year = 2008,
  volume = 113,
  eid = {E00B13},
  pages = {E00B13},
  abstract = {{An analysis of near-infrared emissions on the nightside of Venus
observed by the Visible and Infrared Thermal Imaging Spectrometer
(VIRTIS) instrument on board Venus Express reveals anomalous cloud
particles in the polar regions of Venus. These anomalous particles are
found within the centers of polar vortices at both poles and are either
larger or different in composition from those elsewhere in the planet.
We find no persistent latitudinal variation in cloud properties at low
to midlatitudes, nor do we find asymmetry between the southern and
northern hemispheres. These findings arise from analysis of the relative
brightness of 1.74 and 2.30 {$\mu$}m infrared radiation thermally emitted
from the deep atmosphere of Venus. Larger cloud particles cause
relatively more attenuation at 2.30 {$\mu$}m than at 1.74 {$\mu$}m, so we use
a ``size parameter,'' m = (I $_{1.74mum}$)/(I
$_{2.30mum}$)$^{0.53}$, as a proxy for particle size. This
methodology follows that of Carlson et al. (1993), supported by new
radiative transfer modeling.
  doi = {10.1029/2008JE003108},
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  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},
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  author = {{Spiga}, A. and {Teitelbaum}, H. and {Zeitlin}, V.},
  title = {{Identification of the sources of inertia-gravity waves in the Andes Cordillera region}},
  journal = {Annales Geophysicae},
  year = 2008,
  volume = 26,
  pages = {2551-2568},
  abstract = {{Four major sources of inertia-gravity waves are known in the Earth
atmosphere: upper-tropospheric jet-streams, lower-tropospheric fronts,
convection and topography. The Andes Cordillera region is an area where
all of these major sources are potentially present. By combining ECMWF
and NCEP-NCAR reanalysis, satellite and radiosoundings data and
mesoscale WRF simulations in the Andes Cordillera region, we were able
to identify the cases where, respectively, the jet-stream source, the
convective source and the topography source are predominantly in action.
We retrieve emitted wave parameters for each case, compare them, and
analyse possible emission mechanisms. The WRF mesoscale model shows very
good performance in reproducing the inertia-gravity waves identified in
the data analysis, and assessing their likely sources.
  doi = {10.5194/angeo-26-2551-2008},
  adsurl = {},
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  author = {{Lefèvre}, F. and {Bertaux}, J.-L. and {Clancy}, R.~T. and 
	{Encrenaz}, T. and {Fast}, K. and {Forget}, F. and {Lebonnois}, S. and 
	{Montmessin}, F. and {Perrier}, S.},
  title = {{Heterogeneous chemistry in the atmosphere of Mars}},
  journal = {\nat},
  year = 2008,
  volume = 454,
  pages = {971-975},
  abstract = {{Hydrogen radicals are produced in the martian atmosphere by the
photolysis of water vapour and subsequently initiate catalytic cycles
that recycle carbon dioxide from its photolysis product carbon monoxide.
These processes provide a qualitative explanation for the stability of
the atmosphere of Mars, which contains 95 per cent carbon dioxide.
Balancing carbon dioxide production and loss based on our current
understanding of the gas-phase chemistry in the martian atmosphere has,
however, proven to be difficult. Interactions between gaseous chemical
species and ice cloud particles have been shown to be key factors in the
loss of polar ozone observed in the Earth's stratosphere, and may
significantly perturb the chemistry of the Earth's upper troposphere.
Water-ice clouds are also commonly observed in the atmosphere of Mars
and it has been suggested previously that heterogeneous chemistry could
have an important impact on the composition of the martian atmosphere.
Here we use a state-of-the-art general circulation model together with
new observations of the martian ozone layer to show that model
simulations that include chemical reactions occurring on ice clouds lead
to much improved quantitative agreement with observed martian ozone
levels in comparison with model simulations based on gas-phase chemistry
alone. Ozone is readily destroyed by hydrogen radicals and is therefore
a sensitive tracer of the chemistry that regulates the atmosphere of
Mars. Our results suggest that heterogeneous chemistry on ice clouds
plays an important role in controlling the stability and composition of
the martian atmosphere.
  doi = {10.1038/nature07116},
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  author = {{Spiga}, A. and {Forget}, F.},
  title = {{Fast and accurate estimation of solar irradiance on Martian slopes}},
  journal = {\grl},
  keywords = {Atmospheric Processes: Radiative processes, Planetary Sciences: Solar System Objects: Mars, Atmospheric Composition and Structure: Planetary atmospheres (5210, 5405, 5704), Atmospheric Composition and Structure: Radiation: transmission and scattering, Atmospheric Processes: Instruments and techniques},
  year = 2008,
  volume = 35,
  eid = {L15201},
  pages = {L15201},
  abstract = {{A general parameterization is proposed in this study to calculate, in a
Mars-like dusty atmosphere, the solar irradiance reaching an inclined
surface, assuming the value in the horizontal case is known. Complete
Monte-Carlo radiative transfer calculations, using the Ockert-Bell et
al. (1997) dust optical properties, enable the validation of the method
for Mars. The total shortwave flux reaching the surface is composed of
three contributions: direct incoming flux, reflected flux by surrounding
terrains, and scattered flux by the atmospheric dust. The main
difficulty is the parameterization of the latter component. We show that
the scattered flux reaching the slope can be expressed by a
physically-based simple formula involving one empirical coupling matrix
and two vectors accounting for the scattering properties and the
geometrical settings. The final result is a computationally efficient
parameterization, with an accuracy in most cases better than 5
W.m$^{-2}$. Such a fast and accurate method to calculate solar
irradiance on Martian slopes (should they be topographical surfaces or
solar panels) is of particular interest in a wide range of applications,
such as remote-sensing measurements, geological and meteorological
models, and Mars exploration missions design.
  doi = {10.1029/2008GL034956},
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  author = {{S{\'a}nchez-Lavega}, A. and {Hueso}, R. and {Piccioni}, G. and 
	{Drossart}, P. and {Peralta}, J. and {Pérez-Hoyos}, S. and 
	{Wilson}, C.~F. and {Taylor}, F.~W. and {Baines}, K.~H. and 
	{Luz}, D. and {Erard}, S. and {Lebonnois}, S.},
  title = {{Variable winds on Venus mapped in three dimensions}},
  journal = {\grl},
  keywords = {Atmospheric Composition and Structure: Planetary atmospheres (5210, 5405, 5704), Planetary Sciences: Solar System Objects: Venus, Atmospheric Processes: General circulation (1223), Atmospheric Processes: Planetary meteorology (5445, 5739)},
  year = 2008,
  volume = 35,
  eid = {L13204},
  pages = {L13204},
  abstract = {{We present zonal and meridional wind measurements at three altitude
levels within the cloud layers of Venus from cloud tracking using images
taken with the VIRTIS instrument on board Venus Express. At low
latitudes, zonal winds in the Southern hemisphere are nearly constant
with latitude with westward velocities of 105 ms$^{-1}$ at
cloud-tops (altitude \~{} 66 km) and 60-70 ms$^{-1}$ at the
cloud-base (altitude \~{} 47 km). At high latitudes, zonal wind speeds
decrease linearly with latitude with no detectable vertical wind shear
(values lower than 15 ms$^{-1}$), indicating the possibility of a
vertically coherent vortex structure. Meridional winds at the cloud-tops
are poleward with peak speed of 10 ms$^{-1}$ at 55{\deg} S but
below the cloud tops and averaged over the South hemisphere are found to
be smaller than 5 ms$^{-1}$. We also report the detection at
subpolar latitudes of wind variability due to the solar tide.
  doi = {10.1029/2008GL033817},
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  author = {{Encrenaz}, T. and {Greathouse}, T.~K. and {Richter}, M.~J. and 
	{Bézard}, B. and {Fouchet}, T. and {Lefèvre}, F. and 
	{Montmessin}, F. and {Forget}, F. and {Lebonnois}, S. and {Atreya}, S.~K.
  title = {{Simultaneous mapping of H $_{2}$O and H $_{2}$O $_{2}$ on Mars from infrared high-resolution imaging spectroscopy}},
  journal = {\icarus},
  year = 2008,
  volume = 195,
  pages = {547-556},
  abstract = {{New maps of martian water vapor and hydrogen peroxide have been obtained
in November-December 2005, using the Texas Echelon Cross Echelle
Spectrograph (TEXES) at the NASA Infra Red Telescope facility (IRTF) at
Mauna Kea Observatory. The solar longitude L was 332{\deg} (end of
southern summer). Data have been obtained at 1235-1243 cm $^{-1}$,
with a spectral resolution of 0.016 cm $^{-1}$ ( R=8{\times}10).
The mean water vapor mixing ratio in the region [0{\deg}-55{\deg} S;
345{\deg}-45{\deg} W], at the evening limb, is 150{\plusmn}50 ppm
(corresponding to a column density of 8.3{\plusmn}2.8 pr-{$\mu$}m). The mean
water vapor abundance derived from our measurements is in global overall
agreement with the TES and Mars Express results, as well as the GCM
models, however its spatial distribution looks different from the GCM
predictions, with evidence for an enhancement at low latitudes toward
the evening side. The inferred mean H $_{2}$O $_{2}$
abundance is 15{\plusmn}10 ppb, which is significantly lower than the
June 2003 result [Encrenaz, T., Bézard, B., Greathouse, T.K.,
Richter, M.J., Lacy, J.H., Atreya, S.K., Wong, A.S., Lebonnois, S.,
Lefèvre, F., Forget, F., 2004. Icarus 170, 424-429] and lower
than expected from the photochemical models, taking in account the
change in season. Its spatial distribution shows some similarities with
the map predicted by the GCM but the discrepancy in the H $_{2}$O
$_{2}$ abundance remains to be understood and modeled.
  doi = {10.1016/j.icarus.2008.01.022},
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  author = {{Encrenaz}, T. and {Fouchet}, T. and {Melchiorri}, R. and {Drossart}, P. and 
	{Gondet}, B. and {Langevin}, Y. and {Bibring}, J.-P. and {Forget}, F. and 
	{Maltagliati}, L. and {Titov}, D. and {Formisano}, V.},
  title = {{A study of the Martian water vapor over Hellas using OMEGA and PFS aboard Mars Express}},
  journal = {\aap},
  keywords = {planets and satellites: individual: Mars, infrared: solar system},
  year = 2008,
  volume = 484,
  pages = {547-553},
  abstract = {{We used the OMEGA imaging spectrometer aboard Mars Express to study the
evolution of the water vapor abundance over the Hellas basin, as a
function of the seasonal cycle. The H2O column density is found to range
from very low values (between southern fall and winter) up to more than
15 pr-{$\mu$}m during southern spring and summer. The general behavior is
consistent with the expected seasonal cycle of water vapor on Mars, as
previously observed by TES and modeled. In particular, the maximum water
vapor content is observed around the southern solstice, and is
significantly less than its northern couterpart. However, there is a
noticeable discrepancy around the northern spring equinox (L$_{s}$
= 330-60{\deg}), where the observed H2O column densities are
significantly lower than the values predicted by the GCM. Our data show
an abrupt enhancement of the water vapor column density (from 3 to 16
pr-{$\mu$}m) on a timescale of 3 days, for L$_{s}$ = 251-254{\deg}.
Such an increase, not predicted by the GCM, was also occasionally
observed by TES over Hellas during previous martian years at the same
season; however, its origin remains to be understood.
  doi = {10.1051/0004-6361:20079288},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Fouchet}, T. and {Guerlet}, S. and {Strobel}, D.~F. and {Simon-Miller}, A.~A. and 
	{Bézard}, B. and {Flasar}, F.~M.},
  title = {{An equatorial oscillation in Saturn's middle atmosphere}},
  journal = {\nat},
  year = 2008,
  volume = 453,
  pages = {200-202},
  abstract = {{The middle atmospheres of planets are driven by a combination of
radiative heating and cooling, mean meridional motions, and vertically
propagating waves (which originate in the deep troposphere). It is very
difficult to model these effects and, therefore, observations are
essential to advancing our understanding of atmospheres. The equatorial
stratospheres of Earth and Jupiter oscillate quasi-periodically on
timescales of about two and four years, respectively, driven by
wave-induced momentum transport. On Venus and Titan, waves originating
from surface-atmosphere interaction and inertial instability are thought
to drive the atmosphere to rotate more rapidly than the surface
(superrotation). However, the relevant wave modes have not yet been
precisely identified. Here we report infrared observations showing that
Saturn has an equatorial oscillation like those found on Earth and
Jupiter, as well as a mid-latitude subsidence that may be associated
with the equatorial motion. The latitudinal extent of Saturn's
oscillation shows that it obeys the same basic physics as do those on
Earth and Jupiter. Future highly resolved observations of the
temperature profile together with modelling of these three different
atmospheres will allow us determine the wave mode, the wavelength and
the wave amplitude that lead to middle atmosphere oscillation.
  doi = {10.1038/nature06912},
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  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
  doi = {10.1016/j.icarus.2007.08.030},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Maltagliati}, L. and {Titov}, D.~V. and {Encrenaz}, T. and 
	{Melchiorri}, R. and {Forget}, F. and {Garcia-Comas}, M. and 
	{Keller}, H.~U. and {Langevin}, Y. and {Bibring}, J.-P.},
  title = {{Observations of atmospheric water vapor above the Tharsis volcanoes on Mars with the OMEGA/MEx imaging spectrometer}},
  journal = {\icarus},
  year = 2008,
  volume = 194,
  pages = {53-64},
  abstract = {{The OMEGA imaging spectrometer onboard the Mars Express spacecraft is
particularly well suited to study in detail specific regions of Mars,
thanks to its high spatial resolution and its high signal-to-noise
ratio. We investigate the behavior of atmospheric water vapor over the
four big volcanoes located on the Tharsis plateau (Olympus, Ascraeus,
Pavonis and Arsia Mons) using the 2.6 {$\mu$}m band, which is the strongest
and most sensitive H $_{2}$O band in the OMEGA spectral range. Our
data sample covers the end of MY26 and the whole MY27, with gaps only in
the late northern spring and in northern autumn. The most striking
result of our retrievals is the increase of water vapor mixing ratio
from the valley to the summit of volcanoes. Corresponding column density
is often almost constant, despite a factor of {\tilde}5 decrease in air
mass from the bottom to the top. This peculiar water enrichment on the
volcanoes is present in 75\% of the orbits in our sample. The seasonal
distribution of such enrichment hints at a seasonal dependence, with a
minimum during the northern summer and a maximum around the northern
spring equinox. The enrichment possibly also has a diurnal trend, being
the orbits with a high degree of enrichment concentrated in the early
morning. However, the season and the solar time of the observations, due
to the motion of the spacecraft, are correlated, then the two
dependences cannot be clearly disentangled. Several orbits exhibit also
spatially localized enrichment structures, usually ring- or
crescent-shaped. We retrieve also the height of the saturation level
over the volcanoes. The results show a strong minimum around the
aphelion season, due to the low temperatures, while it raises quickly
before and after this period. The enrichment is possibly generated by
the local circulation characteristic of the volcano region, which can
transport upslope significant quantities of water vapor. The low
altitude of the saturation level during the early summer can then hinder
the transport of water during this season. The influence of the coupling
between atmosphere and surface, due mainly to the action of the
regoliths, can also contribute partially to the observed phenomenon.
  doi = {10.1016/j.icarus.2007.09.027},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Haberle}, R.~M. and {Forget}, F. and {Colaprete}, A. and {Schaeffer}, J. and 
	{Boynton}, W.~V. and {Kelly}, N.~J. and {Chamberlain}, M.~A.
  title = {{The effect of ground ice on the Martian seasonal CO $_{2}$ cycle}},
  journal = {\planss},
  year = 2008,
  volume = 56,
  pages = {251-255},
  abstract = {{The mostly carbon dioxide (CO $_{2}$) atmosphere of Mars condenses
and sublimes in the polar regions, giving rise to the familiar waxing
and waning of its polar caps. The signature of this seasonal CO
$_{2}$ cycle has been detected in surface pressure measurements
from the Viking and Pathfinder landers. The amount of CO $_{2}$
that condenses during fall and winter is controlled by the net polar
energy loss, which is dominated by emitted infrared radiation from the
cap itself. However, models of the CO $_{2}$ cycle match the
surface pressure data only if the emitted radiation is artificially
suppressed suggesting that they are missing a heat source. Here we show
that the missing heat source is the conducted energy coming from soil
that contains water ice very close to the surface. The presence of ice
significantly increases the thermal conductivity of the ground such that
more of the solar energy absorbed at the surface during summer is
conducted downward into the ground where it is stored and released back
to the surface during fall and winter thereby retarding the CO
$_{2}$ condensation rate. The reduction in the condensation rate
is very sensitive to the depth of the soil/ice interface, which our
models suggest is about 8 cm in the Northern Hemisphere and 11 cm in the
Southern Hemisphere. This is consistent with the detection of
significant amounts of polar ground ice by the Mars Odyssey Gamma Ray
Spectrometer and provides an independent means for assessing how close
to the surface the ice must be. Our results also provide an accurate
determination of the global annual mean size of the atmosphere and cap
CO $_{2}$ reservoirs, which are, respectively, 6.1 and 0.9 hPa.
They also indicate that general circulation models will need to account
for the effect of ground ice in their simulations of the seasonal CO
$_{2}$ cycle.
  doi = {10.1016/j.pss.2007.08.006},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Lebonnois}, S.},
  title = {{The atmospheres of Mars, Venus and Titan: observed and modelled structures}},
  journal = {Acoustical Society of America Journal},
  year = 2008,
  volume = 123,
  pages = {3400},
  doi = {10.1121/1.2934094},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}