1. Introduction: dust

The Martian atmospheric dust 
Characteristics of Martian atmosphere
ex. global dust storm (see right figure)

Atmospheric heat source; absorber of both solar 
and infrared radiation.

Injected from the surface by wind; wind tunnel 
experiments show that the critical value of surface 
wind stress is 0.03 - 0.04 Pa.
Greeley & Iversen, 1985

   
Fig1. HST visible image of "Perfect Storm" on Mars.      
(http://oposite.stsci.edu/pubinfo/pr/2001/31/content/0131b.jpg)  

General Circulation Model (GCM) can not raise dust. 
Sufficient surface wind stress to raise dust from the surface is not obtained under clear sky (ie., dust-free) condition.
ex., Greeley et al., 1993

It is suggested that the surface stress could be supplemented by small-scale wind fluctuations which are not represented in GCM.
Wilson & Hamilton, 1996