Warm dust in the atmosphere prevents clouds

These clouds virtually disappear for months over much of Mars whenever the atmosphere contains warm dust.

Warm dust in the atmosphere prevents water-ice clouds from forming. These clouds virtually disappear for months over much of Mars whenever the atmosphere contains warm dust.

This multi-year plot made using TES data shows an anti-correlation: When the atmosphere becomes dustier (reddish colors, top panel), the amount of water-ice cloudiness (purple color, third panel) dwindles. Also note the year-to-year variations.