pub1995.bib

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@article{1995JGR...10021219F,
  author = {{Forget}, F. and {Hansen}, G.~B. and {Pollack}, J.~B.},
  title = {{Low brightness temperatures of Martian polar caps: CO$_{2}$ clouds or low surface emissivity?}},
  journal = {\jgr},
  keywords = {Planetology: Solid Surface Planets: Physical properties of materials, Planetology: Solid Surface Planets: Meteorology},
  year = 1995,
  volume = 100,
  pages = {21219-21234},
  abstract = {{One of the major surprises from the spacecraft missions to Mars of the
1970s was the finding of anomalously low brightness temperatures in the
winter polar regions, far below the expected CO$_{2}$ frost point.
Since then, many explanations have been advanced for this puzzing
behavior, including the low emissivities of carbon dioxide frost and the
presence of carbon dioxide clouds, but no conclusion has been reached.
We have carefully analyzed the measurements obtained by the Mariner 9
infrared interferometer spectrometer (IRIS) and the Viking infrared
thermal mapper (IRTM). Besides their low brightness temperatures, the
anomalous areas are characterized by their high variability and their
complex spectral signature. Also, there is evidence suggesting that
their ocurrence is related to the condensation of CO$_{2}$ in the
atmosphere. We have used a combination of data analysis and modeling to
compare these observations with simulated spectra obtained with
radiative models of CO$_{2}$ ice clouds and CO$_{2}$ ice
deposits. We show that precipitating CO$_{2}$ cloud with particle
radius larger than 10 {$\mu$}m and CO$_{2}$ snow deposits with
millimeter-sized grains are able to produce the observed features. In
both cases, matching the IRIS spectra requires the CO$_{2}$ ice
particles to be mixed with small amounts of water or dust, as expected
for the northern winter cap observed by the Mariner 9 mission.
Nonprecipitating CO$_{2}$ clouds, if they exist, should be
transparent in the infrared. On the other hand, CO$_{2}$ ice
deposits composed of large grains or monolithic ice which have directly
condensed on the ground could have an emissivity close to unity and in
any case much higher than that of small CO$_{2}$ ice particles
originating from atmospheric condensation. We conclude that the low
brightness temperatures are likely to be created by CO$_{2}$ snow
falls and that both falling particles and fresh snow deposits could
contribute to create the observed features. .
}},
  doi = {10.1029/95JE02378},
  adsurl = {http://adsabs.harvard.edu/abs/1995JGR...10021219F},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
@article{1995JGR...100.5501H,
  author = {{Hourdin}, F. and {Forget}, F. and {Talagrand}, O.},
  title = {{The sensitivity of the Martian surface pressure and atmospheric mass budget to various parameters: A comparison between numerical simulations and Viking observations}},
  journal = {\jgr},
  keywords = {Atmospheric Circulation, Atmospheric Models, Atmospheric Pressure, Comparison, Mars Atmosphere, Mass Flow, Albedo, Annual Variations, Data Reduction, Optical Thickness, Surface Roughness, Thermal Emission, Topography},
  year = 1995,
  volume = 100,
  pages = {5501-5523},
  abstract = {{The sensitvity of the Martian atmospheric circulation to a number of
poorly known or strongly varying parameters (surface roughness length,
atmospheric optical depth, CO2 ice albedo, and thermal emissivity) is
investigated through experiments performed with the Martian version of
the atmospheric general circulation model of Laboratoire de Meteorologie
Dynamique, with a rather coarse horizontal resolution (a grid with 32
points in longitude and 24 points in latitude). The results are
evaluated primarily on the basis of comparisons with the surface
pressure records of the Viking mission. To that end, the records are
decomposed into long-period seasonal variations due to mass exchange
with the polar caps and latitudinal redistribution of mass, and
short-period variations due to transient longitudinally propagating
waves. The sensitivty experiments include a 5-year control simulation
and shorter simulations (a little longer than 1 year) performed with
'perturbed' parameter values. The main conclusions are that (1) a change
of horizontal resolution (twice as many points in each direction) mostly
affects the transient waves, (2) surface roughness lengths have a
significant impact on the near-suface wind and, as a matter of
consequence, on the latitudinal redistribution of mass, (3) atmospheric
dust optical depth has a significant impact on radiative balance and
dynamics, and (4) CO2 ice albedo and thermal emissivity strongly
influence mass exchange between the atmosphere and the polar caps. In
view of this last conclusion, an automatic procedure is implemented
through which the albedo and emissivity of each of the two polar caps
are determined, together with the total (i.e., including the caps)
atmospheric CO2 content, in such a way as to get the closest fit of the
model to the Viking pressure measurements.
}},
  doi = {10.1029/94JE03079},
  adsurl = {http://adsabs.harvard.edu/abs/1995JGR...100.5501H},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}