Geoscience Reference
In-Depth Information
Global dust storms are the characteristic phenomena in the Martian
meteorology. They occur only around the Martian perihelion, in southern
springs or summers, although not on every Martian perihelion. Observa-
tions by the Mars-orbiting thermal emission spectrometer onboard Mars
global surveyor (MGS-TES) revealed that the globally averaged daytime
surface temperature decreased by
∼
20 K during the 2001 global dust storm,
whereas the globally averaged daytime atmospheric temperature at 0.5 hPa
(
40 K.
2
The Earth-orbiting submillimeter wave astronomy satellite (SWAS) also
observed the globally averaged surface temperature and vertical atmospheric
temperature profiles of Mars during the onset of the 2001 global dust storm
between
L
s
= 166 and 233
◦
.
3
The peculiar features of Martian tempera-
ture observations in the submillimeter range are that the source function is
nearly linear with temperature, and that the scattering and emission by the
dust do not affect temperature retrievals due to the small particle sizes rela-
tive to the observed wavelength (the typical mean diameter of dust particles
is
∼
∼
25 km) increased by
2
µ
m).
4
The latter is important because the temperature measurements
are not contaminated by the large amount of aerosol during storms in the
Martian atmosphere. The observations from SWAS revealed
∼
∼
20 K decrease
in the surface temperature and
40 K increase in the atmospheric temper-
ature at 0.5 hPa during the global dust storm. This is consistent with the
MGS-TES measurements, and indicates that the temperature retrievals of
SWAS are credible. In addition, SWAS can retrieve the atmospheric temper-
ature at altitudes higher (up to 75 km) than MGS-TES (up to
∼
35 km for
nadir-geometry observations).
2
The SWAS measurements showed no global
thermal effects of the storm above the 0.01 hPa (
∼
60 km) level.
3
Temperature inversions are the phenomena which occur on Mars when
the atmospheric temperature increases with height. The averaged over the
visible disk temperature inversion was apparently observed by SWAS during
the global dust storm (Gurwell, personal communication). It is thought that
the inversions are caused by the increased absorption of the solar radiation
by the dust lifted into the air.
In this paper, we use a recently developed general circulation model
(GCM) of the Martian atmosphere
5
to simulate the circulation and tem-
perature under the scenario corresponding to the conditions of the 2001
dust storm, and compare the model results to the SWAS measurements.
Section 2 presents a brief description of the model and the dust sce-
nario employed in the calculations. The results of the simulations are
shown in Sec. 3. The discussion of the accuracy of the model is given
in Sec. 4.
∼
