Dust in the Wind
From the Department of Comparative Planetology:
The planetary sciences are deeply rooted in the belief that the planets are shaped by common forces. Indeed one of the justifications often cited for studying the other planets is the notion that we will come to better understand how the Earth itself works. At times, however, the diversity of planetary phenomena seems to be too bizarre to have much in common with our home world: The odd surface features on Venus, the raging volcanism of Io and the possibility of a global subsurface ocean on Europa are just a little too "other worldly." So it must be a relief for grant-seeking planetary scientists when they find that something on another planet has an analogue here on the Earth.
Two recent images of giant dust storms on Mars (left) and the Earth (right) are, in fact, eerily similar. Both images (here reproduced at the same scale) show a storm moving as a front with a central jet and marginal vortices—vaguely reminiscent of a mushroom cap. The Martian storm extends about 900 kilometers from the north polar frost cap as seen on August 29 (springtime in the northern hemisphere). The terrestrial storm, blown up from the Sahara Desert in February, extends about 1,800 kilometers off the northwestern coast of Africa.
Giant dust storms have dramatic consequences for the environments of both planets. On Mars a major dust storm may disrupt regional weather patterns or even alter the planet's total heat balance. Aside from altering seasonal weather patterns on the Earth, the Saharan dust storms are thought to have nasty effects on coral reefs in the Caribbean, which have suffered various diseases that appear to be linked to the fall-out of the African dust. The current absence of coral reefs on Mars shouldn't discourage scientists: There must be a grant in here somewhere.