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A direct numerical simulation of thermal convection in the Martian
lower atmosphere is performed by using a two-dimensional anelastic
model.
The results of the simulations reveal that the thermal convection in
the Martian lower atmosphere is km-size convection.
In the case of the dust-free condition, the maximum vertical and
horizontal scales of convective cells are 10 km and 5 km, respectively.
The values of both horizontal and vertical wind
velocity is about 20 m/sec.
It can be estimated by work done by ascending convective plume.
The instantaneous maximum value of the surface stress associated with
the km-size thermal convection in the dust-free case is 0.03 ∼ 0.04 Pa,
which is equal to the threshold value to raise dust from the
surface obtained experimentally.
This result indicates that, the Martian general circulation models
(GCMs), which have not been able to inject dust into the
atmosphere, are now expected to simulate dust injection and the
occurrence of global dust storm self-consistently by parameterizing
the surface stress contribution associated with the km-size thermal
convection.
When dust is allowed to be injected into the atmosphere, dust spreads
into the convective layer promptly and is well mixed within a few hours.
The circulation structure of convection is similar to those of
the dust-free case.
It suggest that horizontal contrast of radiative heating due to that
of dust distribution between updraft region and the other seems to
have no effect on the convection at the time.
Dust can be considered as a passive tracer during dust injection occurs.
After dust is well mixed, the depth of
the convection layer becomes shallower
This is because the stratospheric temperature increases due to the
absorption of solar radiation by dust.
The aspect ratio of ceonvective cell is similar to those observed in
the dust-free case.
The intensity of convetive wind becomes smaller than those of the
dust-free case.
This is because the depth of the convection layer and the potential
temperature deviation of convective plume become smaller.
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