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4.a. Features of Dust Mixing (1)
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Figure 10a: (Upper panel) Dust mixing ratio (kg/kg). Mixing
ratios larger than 1.0×10-8 kg/kg are plotted. (Lower
panel) Vertical wind velocity (m sec-1). Contour interval is 5 m
sec-1. All results are snapshot values from 11:39
to 18:00 LT on day 1 after dust injection initiation every 10 minutes.
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Figure 10a (upper panel) shows dust mixing
ratio for the first day after dust injection is initiated (day
1). Dust is well mixed within 2 to 3 hours by convective
plumes. Immediately after dust injection is initiated, a large dust
mixing ratio is observed within regions of ascending air, and in
particular, within convective plumes. At around 14:00 LT, about two
hours after initiation, dust spreads throughout the entire convection
layer. At 17:00 LT, the distribution of dust below 10 km becomes
almost horizontally and vertically uniform.
During the development stage of dust mixing, there may be an effect of
differential radiative heating between the ascending regions where
dust mixing ratio is large and other regions where the ratio is
small. However, differential heating does not seem to have large
effects on the circulation patterns of convection. Similar to the
results of the dust-free case (Figure 4
(upper right)), the aspect ratio of a convective cell is still
approximately 2 to 1, and the width of an updraft region is almost
equal to that of a downdraft (Figure 10a (lower
panel)). It can be observed that, due to the dust absorption of
solar radiation, the intensity of a downdraft may be slightly reduced
when compared to that of an updraft. However, the amount of decrease,
if any, is only within a range which would require detailed analysis
to show its statistical significance. Results indicate that, before
the contrast of radiative heat affects the circulation pattern of
convection, dust spreads throughout the entire convection layer, and
consequently, its effect is weakened. Dust can be regarded as a
passive tracer during the stage of dust injection and mixing.
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