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and 0.05 hPa atmospheric temperature are consistent with the observations.
These observed features cannot be reproduced in the control run with the
dust radiation scheme turned off. At 0.005 hPa, the temperature changes
little during the global dust storm. This agrees well with observations. At
0.5 hPa, the simulated temperatures rises with the onset of the storm, but
remain lower than in the observations.
There are several possible reasons which may explain these inconsisten-
cies. First, the lack of measurements of the dust parameters results in the
uncertainty in prescribing the dust in the model. There is a wide range
of the observed aerosol particle distributions.
4
Thesizehasaprofound
effect on the radiative transfer, and the corresponding heating/cooling
rates. Besides, there are no measurements concerning the vertical dust
distribution. Therefore, the dust parameters prescribed in Martian GCMs
still represent a very crude approximation, and should be treated cautiously.
Further observations are required.
Second, possible improvements in model results can be expected if the
radiative transfer in the 15
µ
mCO
2
band due to the CO
2
and the dust is
considered interactively, unlike in all Martian GCMs we are aware of. Third,
at lower altitudes, the determination of height in observations becomes
dicult, and the corresponding error increases. More care should be applied
in treating the results from the layers close to the surface.
Acknowledgment
This work was supported by Deutsche Forschungsgemeinschaft (DFG),
project HA 3261/1-2. The authors are grateful to Dr. Teruyuki Nakajima
for providing the parts of the dust radiation code.
References
1. NASA, J. Bell, M. Wolff and the Hubble Heritage Team, Scientists track
“perfect storm” on Mars,
HubbleSite
, STScI-2001-31, 2001.
2. M. D. Smith, Interannual variability in TES atmospheric observations of
Mars during 1999-2003,
Icarus
167
(2004) 148.
3. M. A. Gurwell, E. A. Bergin, G. J. Melnick and V. Tolls, Mars surface and
atmospheric temperature during the 2001 global dust storm,
Icarus
175
(2005) 23.
4. M. G. Tomasko, L. R. Doose, M. Lemmon, P. H. Smith and E. Wegryn, Prop-
erties of dust in the Martian atmosphere from the imager on Mars Pathfinder,
J. Geophys. Res.
104
(1999) 8987.
