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Figure 6.11
Photomosaic of haze over the Nile River Delta. Cairo, at the apex of the Nile delta in the lower half of the mosaic, is invisible beneath a blanket of haze. Under clear weather conditions, the city is visible (inset: arrows indicate north and south margins of city). Two white smoke plumes rise from the region of Helwan, south of Cairo, indicating that the ambient wind is from the west-northwest (top left towards bottom right) on this day. The regular, wavy structure on the surface of the pollution haze (top right) is transverse to the wind direction and appears to be a sequence of "gravity waves," features commonly developed between air layers of differing density (some waves are capped by small cumulus clouds, top right). South of the delta, removed from sources of the haze, the green floor of the Nile valley and the Faiyum depression (bottom left) appear distinctly clearer. [Mosaic of NASA photographs taken August 5, 1997, Hasselblad camera, 250 mm lens, altitude 383 km; NASA5-707-53 (upper), 15:39:01 GMT, center point 30.5N 31E, craft nadir 30.5N 36.0E; NASA5-707-52 (lower), 15:38:46 GMT, center point 30N 31E, craft nadir 29.8N 35.2E. Inset STS084-310-36, May 22, 1997, 05:49:49 GMT, center point 45N 10E, craft nadir 45.9N 14.5E, Hasselblad camera, 100 mm lens, altitude 372 km.]