2. Introduction: thermal convection 

Radiatively driven thermal convection 
One of the wind fluctuations which are not represented in GCM.

It may produce sufficient surface wind stress to raise dust from the surface. 

The thermal convection in Martian lower atmosphere 
has not been examined well.
The depth of convection layer has been calculated by 1-D model.
It is about 8 km under dust free condition (Pollack et el., 1979)
It is about 5 km under dusty condition (visible optical depth of dust is 0.3, Savijarvi, 1991)
The depth of convection layer is also estimated by 1-D convective parameterization in GCM (which is about 6 km, Haberle et al., 1993).

The magnitudes of convective wind velocity and surface stress are unknown.
The magnitude of wind velocity estimated by 1-D model (a few m/sec, Gierash & Goody, 1968) is not the magnitude for the fluctuation of horizontal wind velocity near the surface.

The circulation characteristics of thermal convection is also unknown.