pub2002.bib

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@article{2002JGRE..107.5124N,
  author = {{Newman}, C.~E. and {Lewis}, S.~R. and {Read}, P.~L. and {Forget}, F.
	},
  title = {{Modeling the Martian dust cycle 2. Multiannual radiatively active dust transport simulations}},
  journal = {Journal of Geophysical Research (Planets)},
  keywords = {Atmospheric Composition and Structure: Planetary atmospheres (5405, 5407, 5409, 5704, 5705, 5707), Meteorology and Atmospheric Dynamics: Planetary meteorology (5445, 5739), Planetary Sciences: Atmospheres-structure and dynamics, Atmospheric Composition and Structure: Aerosols and particles (0345, 4801), Planetary Sciences: Meteorology (3346),},
  year = 2002,
  volume = 107,
  eid = {5124},
  pages = {5124},
  abstract = {{Multiannual dust transport simulations have been performed using a Mars
general circulation model containing a dust transport scheme which
responds to changes in the atmospheric state. If the dust transport is
``radiatively active,'' the atmospheric state also responds to changes
in the dust distribution. This paper examines the suspended dust
distribution obtained using different lifting parameterizations,
including an analysis of dust storms produced spontaneously during these
simulations. The lifting mechanisms selected are lifting by (1)
near-surface wind stress and (2) convective vortices known as dust
devils. Each mechanism is separated into two types of parameterization:
threshold-sensitive and -insensitive. The latter produce largely
unrealistic annual dust cycles and storms, and no significant
interannual variability. The threshold-sensitive parameterizations
produce more realistic annual and interannual behavior, as well as
storms with similarities to observed events, thus providing insight into
how real Martian dust storms may develop. Simulations for which dust
devil lifting dominates are too dusty during northern summer. This
suggests either that a removal mechanism (such as dust scavenging by
water ice) reduces opacities at this time or that dust devils are not
the primary mechanism for storm production. Simulations for which
near-surface wind stress lifting dominates produce the observed low
opacities during northern spring/summer, yet appear unable to produce
realistic global storms without storm decay being prevented by the
occurrence of large-scale positive feedbacks on further lifting.
Simulated dust levels are generally linked closely to the seasonal state
of the atmosphere, and no simulation produces the observed amount of
interannual variability.
}},
  doi = {10.1029/2002JE001920},
  adsurl = {http://adsabs.harvard.edu/abs/2002JGRE..107.5124N},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2002JGRE..107.5123N,
  author = {{Newman}, C.~E. and {Lewis}, S.~R. and {Read}, P.~L. and {Forget}, F.
	},
  title = {{Modeling the Martian dust cycle, 1. Representations of dust transport processes}},
  journal = {Journal of Geophysical Research (Planets)},
  keywords = {Atmospheric Composition and Structure: Planetary atmospheres (5405, 5407, 5409, 5704, 5705, 5707), Meteorology and Atmospheric Dynamics: Planetary meteorology (5445, 5739), Planetary Sciences: Atmospheres-structure and dynamics, Atmospheric Composition and Structure: Aerosols and particles (0345, 4801), Planetary Sciences: Meteorology (3346),},
  year = 2002,
  volume = 107,
  eid = {5123},
  pages = {5123},
  abstract = {{A dust transport scheme has been developed for a general circulation
model of the Martian atmosphere. This enables radiatively active dust
transport, with the atmospheric state responding to changes in the dust
distribution via atmospheric heating, as well as dust transport being
determined by atmospheric conditions. The scheme includes dust lifting,
advection by model winds, atmospheric mixing, and gravitational
sedimentation. Parameterizations of lifting initiated by (1)
near-surface wind stress and (2) convective vortices known as dust
devils are considered. Two parameterizations are defined for each
mechanism and are first investigated offline using data previously
output from the non-dust-transporting model. The threshold-insensitive
parameterizations predict some lifting over most regions, varying
smoothly in space and time. The threshold-sensitive parameterizations
predict lifting only during extreme atmospheric conditions (such as
exceptionally strong winds), so lifting is rarer and more confined to
specific regions and times. Wind stress lifting is predicted to peak
during southern summer, largely between latitudes 15{\deg} and 35{\deg}S,
with maxima also in regions of strong slope winds or thermal contrast
flows. These areas are consistent with observed storm onset regions and
dark streak surface features. Dust devil lifting is also predicted to
peak during southern summer, with a moderate peak during northern
summer. The greatest dust devil lifting occurs in early afternoon,
particularly in the Noachis, Arcadia/Amazonis, Sirenum, and Thaumasia
regions. Radiatively active dust transport experiments reveal strong
positive feedbacks on lifting by near-surface wind stress and negative
feedbacks on lifting by dust devils.
}},
  doi = {10.1029/2002JE001910},
  adsurl = {http://adsabs.harvard.edu/abs/2002JGRE..107.5123N},
  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 = {http://adsabs.harvard.edu/abs/2002Icar..159..505L},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2002JGRE..107.5055V,
  author = {{Van den Acker}, E. and {Van Hoolst}, T. and {de Viron}, O. and 
	{Defraigne}, P. and {Forget}, F. and {Hourdin}, F. and {Dehant}, V.
	},
  title = {{Influence of the seasonal winds and the CO$_{2}$ mass exchange between atmosphere and polar caps on Mars' rotation}},
  journal = {Journal of Geophysical Research (Planets)},
  keywords = {Planetary Sciences: Orbital and rotational dynamics, Planetary Sciences: Interiors (8147), Planetary Sciences: Atmospheres-structure and dynamics, Planetary Sciences: Polar regions,},
  year = 2002,
  volume = 107,
  eid = {5055},
  pages = {5055},
  abstract = {{The Martian atmosphere and the CO$_{2}$ polar ice caps exchange
mass. This exchange, together with the atmospheric response to solar
heating, induces variations of the rotation of Mars. Using the angular
momentum budget equation of the system solid-Mars-atmosphere-polar ice
caps, the variations of Mars' rotation can be deduced from the
variations of the angular momentum of the superficial layer; this later
is associated with the winds, that is, the motion term, and with the
mass redistribution, that is, the matter term. For the ``mean'' Martian
atmosphere, without global dust storms, total amplitudes of 10 cm on the
surface are obtained for both the annual and semiannual polar motion
excited by the atmosphere and ice caps. The atmospheric pressure
variations are the dominant contribution to these amplitudes.
Length-of-day (lod) variations have amplitudes of 0.253 ms for the
annual signal and of 0.246 ms for the semiannual signal. The lod
variations are mainly associated with changes in the atmospheric
contribution to the mass term, partly compensated by the polar ice cap
contribution. We computed lod variations and polar motion for three
scenarios having different atmospheric dust contents. The differences
between the three sets of results for lod variations are about one order
of magnitude larger than the expected accuracy of the NEtlander
Ionosphere and Geodesy Experiment (NEIGE) for lod. It will thus be
possible to constrain the global atmospheric circulation models from the
NEIGE measurements.
}},
  doi = {10.1029/2000JE001539},
  adsurl = {http://adsabs.harvard.edu/abs/2002JGRE..107.5055V},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2002Sci...295..110C,
  author = {{Costard}, F. and {Forget}, F. and {Mangold}, N. and {Peulvast}, J.~P.
	},
  title = {{Formation of Recent Martian Debris Flows by Melting of Near-Surface Ground Ice at High Obliquity}},
  journal = {Science},
  year = 2002,
  volume = 295,
  pages = {110-113},
  abstract = {{The observation of small gullies associated with recent surface runoff
on Mars has renewed the question of liquid water stability at the
surface of Mars. The gullies could be formed by groundwater seepage from
underground aquifers; however, observations of gullies originating from
isolated peaks and dune crests question this scenario. We show that
these landforms may result from the melting of water ice in the top few
meters of the martian subsurface at high obliquity. Our conclusions are
based on the analogy between the martian gullies and terrestrial debris
flows observed in Greenland and numerical simulations that show that
above-freezing temperatures can occur at high obliquities in the near
surface of Mars, and that such temperatures are only predicted at
latitudes and for slope orientations corresponding to where the gullies
have been observed on Mars.
}},
  doi = {10.1126/science.295.5552.110},
  adsurl = {http://adsabs.harvard.edu/abs/2002Sci...295..110C},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2002EGSGA..27.6762F,
  author = {{Forget}, F. and {Haberle}, R.~M. and {Marcq}, E. and {Colaprete}, A. and 
	{Schaeffer}, J. and {Wanherdrick}, Y.},
  title = {{Simulation of The Early Mars Climate With A General Circulation Model}},
  journal = {E{\amp}G Quaternary Science Journal},
  year = 2002,
  volume = 27,
  abstract = {{In spite of a solar luminosity significantly lower than it is today,
geological evidence shows that, early in its history during the Noachian
erra, Mars was warm enough to support flowing water. The atmospheric
conditions required to produce and sustain a warm, wet climate on early
Mars remains uncertain. Several models have been used in the past to
study this enigma, but all of them were simple 1D model. To improve our
understanding of the early Mars Climate, we have developped a 3D general
circula- tion model similar to the one used on current Earth or Mars to
study the details of the climate today. To simulate what could have been
the early Mars conditions, we have coupled the Martian General
Circulation model developped at LMD with a sophis- ticated correlated k
distribution model developped at NASA Ames Research Center. As a first
step, we assumed that the early Mars atmosphere was composed of 2 bars
of pure CO2, with CO2 ice clouds possibly condensing in the atmosphere.
Using the correlated k distribution model allowed us to take into
account the complex radiative transfer processes which occur in such an
atmosphere (gaseous and scaterring green- house effect). Preliminary
results suggest that temperature near or above the freezing point of
water could have easily been obtained seasonally in the summer
hemisphere even if the scaterring greenhouse effect of the clouds is
negelected, whereas warming CO2 ice clouds would have especially formed
in the winter hemisphere.
}},
  adsurl = {http://adsabs.harvard.edu/abs/2002EGSGA..27.6762F},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2002EGSGA..27.4812J,
  author = {{Jegou}, F. and {Chassefiere}, E. and {Lellouch}, E. and {Forget}, F. and 
	{Encrenaz}, T. and {Moreno}, R.},
  title = {{Ground-based Millimeter Observations Of The Middle Atmosphere Of Mars}},
  journal = {E{\amp}G Quaternary Science Journal},
  year = 2002,
  volume = 27,
  abstract = {{Measurements of Doppler shift winds and thermal structure of Mars middle
atmo- sphere (40-70 km) have been obtained for ten years from
ground-based millimeter- wave observations. Recently, new measurements
were obtained with I.R.A.M. 30m single dish antenna in april 1999 and in
june 2001. This set of data was completed in april 1999 and in july 2001
by interferometric observations (IRAM Plateau de Bure), with a 5-fold
improvement in spatial resolution.

The Doppler shift wind measurements are of particular interest. The
winds of the middle atmosphere infered from the observations are almost
always retrograde and stronger than expected, compared to the winds
deduced from T.E.S. temperature ob- servations and GCM simulations. This
discrepancy may result from our poor under- standing of the actual
dynamics of the Martian middle atmosphere, but may also be due to the
fact that the measured signal includes some contributions from a large
range of altitude and locations in a way difficult to interpret
directly.

To address this issue we have developed a geometric-radiative transfer
model able to synthesize the CO rotational lines emitted by a 3D varying
temperature wind fields on Mars as it would be observed from Earth. The
synthetic lines can then be compared with the ground-based
millimeter-wave observations.

The model can be applied to GCM simulations, providing a good diagnostic
for the martian GCM in the middle atmosphere, especially with regard to
the interactions between the atmospheric tides and the mean flow.

Indeed, one possible explanation of the strong retrograde jet could be
the effect of the zonal acceleration induced by dissipation of tides in
the mesosphere. A retrograde acceleration due to momentum deposit is
well modeled at low latitudes. Zonal accel- eration results in the
formation of a dynamical meridional cell, from 0 to 30 degrees of
latitude.

Unfortunatly the amplitude and the spread of the jet in the GCM
simulations are too weak compared to the observations. A best
understanding of the dissipation of the tides could bring nearer the
observations and the theory.
}},
  adsurl = {http://adsabs.harvard.edu/abs/2002EGSGA..27.4812J},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2002EGSGA..27.4727F,
  author = {{Forget}, F. and {Beaudin}, G. and {Encrenaz}, A.~D.~P. and 
	{Gheudin}, M. and {Thomas}, B. and {Capderou}, M. and {Dassas}, K. and 
	{Ricaud}, P. and {Urban}, J. and {Gulkis}, M.~F.~S. and {Janssen}, M. and 
	{Riley}, L. and {Encrenaz}, T. and {Lellouch}, E. and {Clancy}, P.~H.~T.
	},
  title = {{Microwave Sounding Of The Martian Atmosphere With Mambo}},
  journal = {E{\amp}G Quaternary Science Journal},
  year = 2002,
  volume = 27,
  abstract = {{Aboard the CNES orbiter currently planned for 2007, the Mars Atmosphere
Mi- crowave Brightness Observer (MAMBO) aims to characterize the water
cycle, the dynamics, and the photo-chemistry of the Martian atmosphere,
with an unprecedented sensitivity and coverage. For this purpose, MAMBO
will analyse the thermal emission of the atmosphere using heterodyne
spectroscopy, for the first time from orbit around another planet. In
practice, MAMBO will be a 20 kg instrument including a 20-25 cm rotating
antenna to perform measurements at the atmospheric limb and at nadir,
with a receiver dedicated to the monitoring of selected lines of key
molecule around 320-350 GHz: H2O, CO, 13CO, HDO, O3, H2O2.

The inversion of CO and 13CO will allow to directly map 3D winds for the
first time on Mars (by Doppler shift, with an accuracy of about 10m/s),
and map the temperature from the surface up to the homopause around 120
km. Combined with data assimila- tion technique, these measurements will
allow us to determine the 3D atmospheric circulation day after day and
perform comparative meteorology. Water vapor profiles will be measured
with an accuracy and a sensitivity much better than any previous ex-
periments. In addition, we will learn about possible fractionation
processes in the wa- ter cycle by monitoring the variations of the D/H
ratio by simultaneous spectroscopy of H2O and HDO. Last, a global view
of the martian atmosphere photochemistry will be obtained by profiling
key species CO, H2O, O3, and H2O2. This last species has never been
observed on Mars. However, several models have shown its key impor-
tance for the chemical equilibrium of the atmosphere and for its role in
oxydizing the martian soil, a problem of key interest for exobiology.
}},
  adsurl = {http://adsabs.harvard.edu/abs/2002EGSGA..27.4727F},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2002EGSGA..27.4588C,
  author = {{Chassefiere}, E. and {Bertaux}, J.-L. and {Berthelier}, J.-J. and 
	{Cerisier}, J.-C. and {Forget}, F. and {Menvielle}, M. and {Hulot}, G. and 
	{Mandea}, M. and {Reme}, H. and {Barriot}, J.-P. and {Blanc}, M. and 
	{Parrot}, M. and {Trotignon}, J.-G. and {Barlier}, F. and {Touboul}, P. and 
	{Lilensten}, J. and {Nagy}, A. and {Bougher}, S. and {Waite}, H. and 
	{Yung}, D. and {Clarke}, J. and {Lin}, R. and {Luhmann}, J. and 
	{Smrekar}, S. and {Purucker}, M. and {Breuer}, D. and {Szego}, K.
	},
  title = {{Dynamo : An Instrumental Suite To Characterize Atmospheric Escape and To Complete Magnetic Field Mapping of Mars From The 07 Cnes Orbiter}},
  journal = {E{\amp}G Quaternary Science Journal},
  year = 2002,
  volume = 27,
  abstract = {{DYNAMO is a suite of instruments to be implemented in the frame of the
NASA/CNES Mars program and planned to be flown onboard the 2007 CNES or-
biter. It is primarily aimed at characterizing current atmospheric
escape, which is still poorly constrained, and at providing a detailed
and complete mapping of the crustal magnetic field. These objectives are
achieved from a low periapsis orbit (150-170 km x 1000 km), during an
extended phase of the mission. They are reached by using a nominal
payload composed of : a low-energy ion and neutral mass spectrometer
measuring the thermal and hot populations, and wind velocities,
complemented by specific sensors of the neutral atmosphere, an energetic
particle spectrometer mea- suring all kinds of particles resulting from
solar wind interaction, according to their nature, flux and velocity
distribution, a Langmuir probe for adequate restitution of the
ionospheric environment, associated with more specific plasma
instruments, a UV airglow spectrometer allowing to probe high exospheric
levels, as well as lower parts of the atmosphere, a 3-axis magnetometer
to measure the static part of the magnetic field vector. A radio science
experiment is under study, in order to measure electron profiles in the
ionosphere, and to improve the resolution of the gravity field.
}},
  adsurl = {http://adsabs.harvard.edu/abs/2002EGSGA..27.4588C},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2002EGSGA..27.4569M,
  author = {{Montmessin}, F. and {Rannou}, P. and {Forget}, F. and {Cabane}, M.
	},
  title = {{Study of Martian Water Ice Clouds Using A General Circulation Model}},
  journal = {E{\amp}G Quaternary Science Journal},
  year = 2002,
  volume = 27,
  abstract = {{By means of the LMD/MGCM, we investigated the spatial and temporal
variations of water ice clouds in the atmosphere of Mars. We employed a
simplified cloud scheme, where ice particles are submitted to
condensational growth, sublimation, sedimenta- tion and transported by
3D dynamics. Radiative effects of clouds are also accounted for. We
present the results of our simulation, emphasizing the radiative aspect
of clouds and their effects on the global water cycle.
}},
  adsurl = {http://adsabs.harvard.edu/abs/2002EGSGA..27.4569M},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2002EGSGA..27.4418C,
  author = {{Coll}, A.~I.~M. and {Forget}, F. and {Hourdin}, F. and {Wanherdrick}, J. and 
	{Lopez-Valverde}, M.~A. and {Lewis}, S.~R. and {Read}, P.~L.
	},
  title = {{First Results With The Mars Thermospheric Lmd General Circulation Model}},
  journal = {E{\amp}G Quaternary Science Journal},
  year = 2002,
  volume = 27,
  abstract = {{The LMD-AOPP Mars General Circulation Model developed jointly by LMD
(Paris), AOPP (Oxford) and IAA (Granada) has been extended into the
thermosphere. The model reaches a height of approximately 240 km and
includes the effects of thermal conduction, molecular viscosity and EUV
absorption which are relevant processes at high altitudes. The model
also includes non-LTE effects in the upper atmosphere. This is the first
model to be able to simulate the planet's atmosphere from the ground up
to thermospheric heights. This full coupling of the various atmospheric
regions yields an excellent tool to study the effects of lower
atmospheric processes, such as dust storms or upward propagating waves,
on the upper atmosphere. First results of the improved Mars LMD TGCM
will be shown.

This research was funded under CNES and ESTEC Contract 11369/95/NL/JG
}},
  adsurl = {http://adsabs.harvard.edu/abs/2002EGSGA..27.4418C},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2002EGSGA..27.3765L,
  author = {{Lebonnois}, S. and {Hourdin}, F. and {Rannou}, P. and {Luz}, D.
	},
  title = {{Impact of The Seasonal Variations of Ethane and Acetylene Distributions On The Temperature Field of Titan's Stratosphere}},
  journal = {E{\amp}G Quaternary Science Journal},
  year = 2002,
  volume = 27,
  abstract = {{An enrichment has been observed for several compounds in Titan's
stratosphere by IRIS/Voyager 1, for high latitudes coming out of winter
(Coustenis and Bézard, Icarus 115, 1995). Bézard et al.
(Icarus 113, 1995) showed that this enrichment sould be capable of
affecting the temperature field in Titan's stratosphere by inducing a
relative cooling at those latitudes.

The impact of meridional dynamics on the composition of Titan's
atmosphere has been studied recently with a 2-dimensional photochemical
model (Lebonnois et al., Icarus 152, 2001).To go further into the study
of the coupling between photochemistry and dynamics, a photochemical
module has been directly introduced into the general cir- culation model
of the Laboratoire de Météorologie Dynamique (described in
Hourdin et al., Icarus 117, 1995). A simplified module has also been
implemented, that uses for a limited number of species a simple linear
relaxation toward a prescribed vertical profile, instead of the complex
photochemical calculations. This technique, presented in Lebonnois et
al. (2001), allows to reproduce the latitudinal variations observed in
the stratosphere of Titan for some species. We consider here the case of
C2H2 and C2H6, because the distributions of these compounds are taken
into account in the ra- diative calculations of the GCM. The
contributions of other trace compounds have been neglected until now,
based on their equatorial mole fractions.

Using this simplified coupled model, we have studied the impact on the
temperature field of the variations of the distributions of C2H2 and
C2H6 induced by meridional dynamics. The enrichment obtained in the
descending branch of the Hadley cell is associated with a relative
cooling for pressures under approximately 1 mbar (altitudes above 200
km). For lower altitudes, the effect is a slight heating.

We will present these effects and their interpretation, and will discuss
their signifi- cance, especially when compared to the thermal effects of
the coupling between dy- namics and the aerosols' distribution.
}},
  adsurl = {http://adsabs.harvard.edu/abs/2002EGSGA..27.3765L},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2002EGSGA..27.3080M,
  author = {{Mangold}, N. and {Forget}, F. and {Peulvast}, F.~C.~J.-P.},
  title = {{Narrow Gullies Over High Sand Dunes On Mars: Evidence For Recent Liquid Flows}},
  journal = {E{\amp}G Quaternary Science Journal},
  year = 2002,
  volume = 27,
  abstract = {{The discovery of recent gullies on Mars is one of the more unexpected
observation of Mars Global Surveyor. The characteristics of these
landforms suggest the local occurrence of a fluid emanating from alcoves
located mostly in the upper part of poleward-facing slopes at mid and
high latitudes (Malin and Edgett, Science, June 2000). However,
observations of gullies originating from the top of peaks and sand dunes
question this scenario. According to observations related to terrestrial
debris flows analogous to martian gullies, we have shown that most
gullies are more likely to result from the melting of liquid water in
the first meters of the Martian sub- surface (Costard et al., Science,
January 2002). Numerical simulations show that above-freezing
temperatures can occur at high obliquities (? =40-45{\deg}) in the near-
surface of Mars. Here, we focus on gullies observed on the flanks of
high sand dunes. Narrow gullies interpreted as the result of liquid
flows on frozen dunes are observed on 6 MOC images in the latitudes of
40 to 60{\deg}S. Among these dunes, a large scale sand dunes reaching an
elevation of 600 m above surrounding plains covers the floor of Russel
crater. This dune is striped by narrow channels less than 20 m wide and
1 to 2 km long. The sinuousity of several channels shows that the flow
is not very fast (less than 10 m/s) and inconsistent with CO2 driven
flows. Indeed, flows triggered by CO2 would give high velocities
strictly larger than 20 m/s like pyroclastic flows on Earth. Lateral
ridges, also called ``levées'', are observed on every channels like
on terrestrial debris flows. This demonstrates that the liquid of the
flow is a viscous slurry with a given shear strength. These gullies over
dunes are therefore due to flows of liquid water mixed with sand and
dust. This favors an external cause for the occurrence of liquid water
by melting of water ice inside the near-surface porosity of dunes during
a recent period of high obliquity in agreement with temperature
variations found by simulations. The fact that gullies over dunes are
still observable at the present time also shows that dunes may be frozen
and inactive for thousand years explaining the conservation of these
landforms.
}},
  adsurl = {http://adsabs.harvard.edu/abs/2002EGSGA..27.3080M},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{2002AdSpR..29..175M,
  author = {{Markiewicz}, W.~J. and {Keller}, H.~U. and {Thomas}, N. and 
	{Titov}, D. and {Forget}, F.},
  title = {{Optical properties of the Martian aerosols in the visible spectral range}},
  journal = {Advances in Space Research},
  year = 2002,
  volume = 29,
  pages = {175-181},
  abstract = {{Imager for Mars Pathfinder (IMP) obtained data of sky brightness as a
function of the scattering angle, wavelength, time of day and Sol. This
data set is fitted with model calculations to extract the size
distribution, shape and the refractive index of the aerosols suspended
in the atmosphere. The inferred optical parameters are discussed in
context of diurnal variations and compared to those derived from Viking
Landers cameras and Phobos KRFM radiometer data. The effects of the
scattering and absorption of the solar radiation by the atmospheric
aerosols are discussed in terms of their influence on the
spectrophotometry of the Martian surface.
}},
  doi = {10.1016/S0273-1177(01)00567-1},
  adsurl = {http://adsabs.harvard.edu/abs/2002AdSpR..29..175M},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}