Polar Stratospheric Cloud, seen from the NASA DC-8 on 4 February 2003 (photograph by Mark Schoeberl, GSFC). This cloud was formed due to turbulent air motion over Iceland (mountain waves). Lidar measurements revealed the primary cloud was composed of ice (Type 2 PSC). The photograph was taken just at sunrise for the lower atmosphere. Under these conditions, the polar stratospheric cloud is illuminated directly by the sun while the lower atmosphere is still shaded from the direct sunlight, accounting for the brilliant appearance of this cloud. Click here for more information on Polar Stratospheric Clouds