Contrails

Credit: Copyright University Corporation for Atmospheric Research

Jet aircraft flying at high altitudes often produce a trail of condensed vapor called a contrail. The mixing of hot exhaust gases from the engines with cold outside air causes ice crystals to form on particles in the exhaust. A contrail evaporates rapidly when the relative humidity of the surrounding air is low. If the humidity is high, a contrail may stay visible as cirrus-like clouds for many hours.