4. Results: dusty case index previous next
4. Results: dusty case

In the dust-free case, surface stress associated with km-size convection reaches a fairly large value in the afternoon when convective activity becomes the highest (Figure 5). Surface stress in the afternoon cirtainly exceeds the threshold value required to raise dust from the surface, considering a superposition of a large scale background wind on the convective wind (Figure 6). In order to realize dust injection into the atmosphere in our convection model utilized in this study, we have to incorporate a large scale background wind into the model.

However, since

  • it is exepcted that the circulation structure of km-size thermal convection will be affected not only by dust but also by the background wind,
  • it is not desirable to have an effect of large scale background wind on the structure of km-size convection, since we are focusing on the effect of dust on the structure of km-size convection in this study,
in the followings, we do not adapt the model to incorporate a large scale background wind for realizing spontaneous dust injection, but we adopt an artificial setup where the value of the threshold surface stress is adjusted so that dust injection occurs by the wind associated with km-size convection in the afternoon.

The adjusted value of the threshold surface stress is 0.01 Pa. This value is adopted based on the results of the dust-free case that the maximum value of surface stress exceeds 0.01 Pa in the afternoon (Figure 5), and the value of surface stress frequently exceeds 0.01 Pa at several grid points (Figure 6). The initial condition is the result of the dust-free case at LT=6:00 of the 6th day. The numerical integration is performed for 6 days.

Figure 9 shows time development of horizontal mean dust opacity for solar radiation (λ = 0.67 μm). Dust opacity rapidly increases in the first day, and after that, it keeps almost a constant value (about 0.07). In the followings, we show features of dust mixing from the first to second day, and resluts on the 6th day at which the model reaches almost an equilibrium state.

  1. Feature of dust mixing
  2. Horizontal mean fields
  3. Circulation structure of convection

Figure 9: Time development of horizontal mean dust opacity for solar radiation. Horizontal axis denotes numerical integration time from the initial.


A numerical simulation of thermal convection in the Martian lower atmosphere.
Odaka, Nakajima, Ishiwatari, Hayashi,   Nagare Multimedia 2001
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