Changes in Atmospheric Clarity. These two views in violet light illustrate the dramatic change in the clarity of the atmosphere in the region east and northeast of the Argyre basin during winter in the southern hemisphere. This was taken just after the winter solstice when solar heating was minimal. This view was taken in late winter when the area had started to warm. The cold southern regions may trap water vapor from the much warmer northern hemisphere to form these clouds, or water vapor may be released from the seasonal polar cap as it retreats.
North is to the left in both images.