Contrail and Shadow over Devon, England
September 27, 2009
The above photo shows a lengthy jet condensation trail (contrail) and its shadow as seen over Chulmleigh, England (near Devon) on the afternoon of August 8, 2009. Contrails form from the condensation of water vapor in the exhaust of jet engines. In very cold air having low vapor pressure, the increase in the local water vapor from a jet’s exhaust can boost the air’s water content beyond its saturation point. When this occurs, the vapor then condenses into miniscule water droplets and/or ice crystals. The myriad water droplets are observed as a contrail. The longer the contrail the greater the abundance of water vapor at the altitude of the aircraft. On occasion, shadows of contrails can be seen cast on thin, lower clouds. Note that the shadow all but disappears as the contrail passes through a stretch of clear, blue sky. Perspective makes it seem as though the shadow is cast upward.