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4.c. Circulation structure of convection
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Figure 13 shows the circulation structure of
thermal convection of the 6th day of the dusty case.
(See also Appendix D for the results
with a shorter output time interval)
The vertical and horizontal scales of convective cells
are about 5 km and 2 to 3 km, respectively.
Thermal convection realized under the dusty condition
is also km-size as that realized under the dust free condition.
Potential temperature deviation associated with
convective plumes is 1 to 2 K,
which is smaller than that of the dust-free case
(Figure 4 (left upper panel)).
The magnitude of vertical wind velocity is
10 to 15 msec-1, and
that of horizontal wind velocity
is about 10 msec-1.
These values are smaller than those of the same period of
time of the dust-free case
(Figure 4 (right panel)).
The ratio of updraft width to that of downdraft,
the appearance of convective plume migration,
and the way of mixing due to convective plumes
are similar to those observed in the dust-free case.
The reason why the magnitude of wind velocity is small compared to that of
dust free case is the decrease of convection layer thickness
and the decrease of potential temperature deviation of
convective plumes.
Since the length of free acceleration decreases as
the decrease of convective layer thickness,
kinetic energy generation due to buoyancy force
decreases.
Since the depth of convection layer h and
potential temperature deviation of convective plumes
Δθ are about one half of
those in the dust-free case,
the magnitude of wind velocity estimated by (1) is also one half of that
of the dust free case (about 10 msec-1).
Potential temperature deviation associated
with convective plumes can be estimated
by using (5);
the details are shown in section 4.c.i.
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