56 research outputs found
Recommended from our members
MGS accelerometer data analysis with the LMD GCM
Mars Global Surveyor aerobreaking phases, required to
achieve its mapping orbit, have yielded vertical profiles
of thermospheric densities, scale heights and temperatures
covering a broad range of local times, seasons and
spatial coordinates [Keating et al. 1998, 2001]. Phase
I covered local times from 11 to 16 h (assuming 24
"martian hours” per martian day or sols), with a latitude
coverage of approximately 40deg to 60deg N. Seasons
observed during this phase were centered around winter
solstice and altitudes of periapsis range from 115 to
135 km. The altitudes for Phase II were lower, with a
minimum around 100 km and a maximum around 120.
Martian spring was the season covered during this phase
and the local time was between 15 and 16 h. The latitude
covered by Phase II, however, was more extense
than that seen during Phase I, with a coverage from 60deg N
to basically the South Pole
Recommended from our members
Towards a global model of the martian atmosphere
In an effort to continuously improve the capabilities of the Martian atmospheric predictions at LMD, the GCM has been extended into thermospheric heights thus creating the first model to self-consistently couple the lower and upper
regions of the Martian atmosphere. The behaviour of
the Martian thermosphere is strongly influenced by
lower atmospheric processes and has complex dynamics.
Such a fully coupled model will certainly aid in the preparation of future missions and on the analysis of future high altitude data, as well as serve as a base for the simulation of ionospheric processes, escape, etc
Recommended from our members
Modeling of the general circulation with the LMD-AOPP-IAA GCM: Update on model design and comparison with observations
The LMD-AOPP GCM is developed conjointly by LMD in Paris and AOPP in Oxford, with the collaboration of
IAA in Granada for the physical processes specific to the upper atmosphere. The collaboration between the
two teams is based on the use of two different dynamical core (gridpoint at LMD, spectral at AOPP), which
allow us to estimate the likely uncertainty arising from certain types of modeling errors. Similarly, we use
different schemes to compute tracer transport, etc. The work has benefited from support from ESA (since 1995)
and CNES (since 2000). Within that context, the GCMs are used to produce a Martian climate 'database' which
is used by more than 30 teams around the world for mission design and scientific studies (see Bingham et al.,
this issue and Lewis et al., 1999). The baseline version of the GCM is described in detail in Forget et al. (1999). Here we describe the recent improvement and design changes since this publication. Compared to this previous version, the new GCM covers a wider range of altitude, from 0 to 120km in the vertical, it uses improved topography and thermal inertia surface
maps from Mars Global Surveyor (MGS), and includes a new 'dust scenario' to describe the distribution of airborne dust in the atmosphere
Recommended from our members
The Mars Climate Database
The Mars Climate Database (MCD) [1] is a database of statistics describing the climate and environment of the Martian atmosphere. It was constructed directly on the basis of output from mulitannual integrations of two general circulation models (GCMs)developed by Laboratoire de Météorologie Dynamique du CNRS, France, the University of Oxford, UK, and Instituto de Astrofisica de Andalucia, Spain, with support from the European Space Agency (ESA) and Centre National d–Etudes Spatiales (CNES). A description of the MCD is given along with a comparison between spacecraft observations of Mars and results predicted at similar locations and times in the MCD.
The MCD can be used as a tool for mission planning and has been applied to prepare for several missions in Europe and the USA. It also provides information for mission design specialists on the mean state and variability of the Martian environment from the surface to above 120km. The GCMs on which the database is founded, include a set of physical parameterizations (radiative transfer in the visible and thermal infrared ranges, turbulent mixing, condensation-sublimation of CO2, thermal conduction in
the soil and representation of gravity waves) and two
different codes for the representation of large scale
dynamics: a spectral code for the AOPP version and
a grid-point code for the LMD version. The GCMs correctly reproduce the main meteorological features of Mars, as observed by the Mariner 9 and Viking orbiters, the Viking landers, and Mars Global Surveyor (MGS). As well as the standard statistical measures for mission design studies, the MCD includes a novel representation of large-scale variability, using empirical eigenfunctions derived from an
analysis of the full simulations, and small-scale variability based on parameterizations of processes such
as gravity wave propagation. The database allows the user to choose from 5 dust storm scenarios including a best guess, default scenario, deduced from recent MGS observations, an upper boundary for an atmosphere without dust storms, as observed by Viking the landers, and a clear, cold, lower boundary scenario, as observed by Phobos 2 and from Earth. The full version of the MCD is available on CDROM (for UNIX systems and PCs) and is also
accessible through an interactive WWW interface at
http://www-mars.lmd.jussieu.fr/
Radio science measurements of atmospheric refractivity with Mars Global Surveyor
Radio occultation experiments with Mars Global Surveyor measure the refractive index of the Martian atmosphere from the surface to ~250 km in geopotential height. Refractivity is proportional to neutral density at low altitudes and electron density at high altitudes, with a transition at ~75 km. We use weighted least squares to decompose zonal refractivity variations into amplitudes and phases for observed wave numbers k=1-4 over the entire altitude range and use the results to analyze atmospheric structure and dynamics. The data set consists of 147 refractivity profiles acquired in December 2000 at summer solstice in the Martian northern hemisphere. The measurements are at an essentially fixed local time (sunrise) and at latitudes from 67deg to 70degN. Thermal tides appear to be responsible for much of the observed ionospheric structure from 80 to 220 km. Tides modulate the neutral density, which in turn, controls the height at which the ionosphere forms. The resulting longitude-dependent vertical displacement of the ionosphere generates distinctive structure in the fitted amplitudes, particularly at k=3, within plusmn50 km of the electron density peak height. Our k=3 observations are consistent with an eastward propagating semidiurnal tide with zonal wave number 1. Relative to previous results, our analysis extends the characterization of tides to altitudes well above and below the electron density peak. In the neutral atmosphere, refractivity variations from the surface to 50 km appear to arise from stationary Rossby waves. Upon examining the full vertical range, stationary waves appear to dominate altitudes below ~75 km, and thermal tides dominate altitudes above this transition region
Vertical dust mixing and the interannual variations in the Mars thermosphere
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94815/1/jgre2303.pd
New near-IR observations of mesospheric CO2 and H2O clouds on Mars
Carbon dioxide clouds, which are speculated by models on solar and
extra-solar planets, have been recently observed near the equator of Mars. The
most comprehensive identification of Martian CO2 ice clouds has been obtained
by the near-IR imaging spectrometer OMEGA. CRISM, a similar instrument with a
higher spatial resolution, cannot detect these clouds with the same method due
to its shorter wavelength range. Here we present a new method to detect CO2
clouds using near-IR data based on the comparison of H2O and CO2 ice spectral
properties. The spatial and seasonal distributions of 54 CRISM observations
containing CO2 clouds are reported, in addition to 17 new OMEGA observations.
CRISM CO2 clouds are characterized by grain size in the 0.5-2\mum range and
optical depths lower than 0.3. The distributions of CO2 clouds inferred from
OMEGA and CRISM are consistent with each other and match at first order the
distribution of high altitude (>60km) clouds derived from previous studies. At
second order, discrepancies are observed. We report the identification of H2O
clouds extending up to 80 km altitude, which could explain part of these
discrepancies: both CO2 and H2O clouds can exist at high, mesospheric
altitudes. CRISM observations of afternoon CO2 clouds display morphologies
resembling terrestrial cirrus, which generalizes a previous result to the whole
equatorial clouds season. Finally, we show that morning OMEGA observations have
been previously misinterpreted as evidence for cumuliform, and hence
potentially convective, CO2 clouds.Comment: Vincendon, M., C. Pilorget, B. Gondet, S. Murchie, and J.-P. Bibring
(2011), New near-IR observations of mesospheric CO2 and H2O clouds on Mars,
J. Geophys. Res., 116, E00J0
Thermal effects of internal gravity waves in the Martian upper atmosphere
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95329/1/grl28981.pd
Four Martian years of nightside upper thermospheric mass densities derived from electron reflectometry: Method extension and comparison with GCM simulations
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95498/1/jgre2766.pd
MGS Radio Science electron density profiles: Interannual variability and implications for the Martian neutral atmosphere
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94869/1/jgre1778.pd
- …