4. Results: Dusty Case
4.a. Features of Dust Mixing (2) Figure 10b : (Upper panel) Dust mixing ratio (kg/kg). Areas with a mixing ratio larger than 1.0×10-8 are colored. (Lower panel) Turbulent diffusion coefficient (m2 sec-1). Areas with a value larger than 1.0×10-5 are colored. All results are for day 2 after dust injection initiation every 1 hour from 7:00 to 18:00 LT. Dust, when mixed and thoroughly distributed up to 10 km, is further transported upward into the stratosphere. Figure 10b (upper panel) shows the distribution of dust mixing ratio for day 2 after dust injection initiation. In the afternoon, at altitudes near 10 km, dust propagates upward in the form of plumes. Distribution of the turbulent diffusion coefficient (Figure 10b (lower panel)) suggests that these plumes are accompanied by a vertical mixing process that differs from that of the kilometer-size thermal convection near the surface. At altitudes near 10 km, vertical mixing is caused by a vertical difference of radiative heating associated with the vertical contrast of dust density. As a result of dust injection and mixing on day 1, a region with a large vertical gradient of dust mixing ratio forms at altitudes from 11 to 13 km (Figure 11a). Associated with this gradient, a large difference of solar radiative heating can be observed in regions below 13 km (Figure 11g, Figure 11h). Consequently, an inversion of potential temperature occurs at a height of approximately 10 km, and the layer between 10 km and 13 km becomes convectively unstable. The vertical distribution of horizontal mean potential temperature (Figure 11d (right panel)) shows that this unstable layer is rapidly stabilized and potential temperature from 10 to 15 km becomes vertically uniform. The upward transport of dust into the stratosphere is a direct result of the heating of dust solar absorption; dust is no longer a passive tracer in this region. The vertical profile of horizontal mean dust mixing ratio does not significantly vary on or after day 4 (Figure 11b). In the convection layer, dust mixing ratio slightly increases as depth of the convection layer decreases. In the region above the convection layer, dust mixing ratio slightly decreases due to the gravitational sedimentation of dust.
Horizontal mean fields during dust injection occurs. Dust mixing ratio (Figure 11a, Figure 11b) Temperature and potential temperature (Figure 11c, Figure 11d) Atmospheric heating profile (Figure 11e, Figure 11f, Figure 11g, Figure 11h)
A numerical simulation of thermal convection in the Martian lower atmosphere with a two-dimensional anelastic model