Hellas Planitia in Winter (Natural Colors; credits: NASA/MGS/MSSS)

"This picture captures two dust storms, each large enough to cover Arizona or New Mexico. One is located near the lower left, the other at the lower right. Taken on April 8, 2001 (Mid-Southern Winter), this is a mosaic of six MOC daily global images centered around Hellas Planitia in the Martian Southern Hemisphere. Hellas Planitia is the dominant elliptical feature just below the center of the picture. The bright, nearly white surfaces along the lower (southern) edge of the picture are covered by wintertime frost. The strong temperature difference between the winter frost and the warmer air just off the edge of this Polar Cap generates winds that - at this time of year - are often strong enough to lift Dust into large, reddish-brown, billowy clouds".