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  author = {{Forget}, F. and {Pollack}, J.~B.},
  title = {{Thermal infrared observations of the condensing Martian polar caps: CO$_{2}$ ice temperatures and radiative budget}},
  journal = {\jgr},
  keywords = {Planetology: Solid Surface Planets: General or miscellaneous, Planetology: Solid Surface Planets: Physical properties of materials, Planetology: Solid Surface Planets: Meteorology},
  year = 1996,
  volume = 101,
  pages = {16865-16880},
  abstract = {{The physical processes that control the formation of the Martian
seasonal polar caps are not completely understood. On the one hand,
climate models reproducing the annual variations in atmospheric pressure
caused by the condensation of the polar caps have shown that the amount
of CO$_{2}$ actually trapped in the polar regions in winter is
lower than expected from simple energy balance considerations. On the
other hand, the available spacecraft observations of the condensing
polar caps are complex and puzzling. They are characterized by highly
variable low-emission zones exhibiting anomalously cold brightness
temperatures. To better understand these results, we have carefully
reanalyzed the Viking infrared thermal mapper (IRTM) measurements
obtained during the polar night in both hemispheres. First, by removing
the signature of the low-emission zones in the data, we have retrieved
the actual surface temperatures of the polar caps. We find that they
were lower than the frost point of CO$_{2}$ for the topography of
the polar regions usually used in models, especially in the south polar
region. However, our analysis reveals that the low-emission zones were
more frequent and more intense in the northern hemisphere. They strongly
altered the polar radiative budget which is computed and analyzed here,
and thus the CO$_{2}$ condensation rate. We conclude that the
models' tendency to overestimate the amount of CO$_{2}$ ice
condensing in the polar caps is explained by different causes in each
hemisphere. In the north, the models did not simulate the low-emission
zones and underestimated the heat advected to the polar cap region
during the dust storms, especially by the upper atmosphere polar
warming. In the south, they overestimated the polar cap surface
temperatures and also did not simulate the low-emission zones.
  doi = {10.1029/96JE01077},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}