September 23, 2002


Provided by: Eleanor Brandli
Summary authors & editors: Hank Brandli; Jim Foster

On most days, jet contrails can be seen cris-crossing the sky - they're easy to detect. However, not such an easy feature to discern is a related phenomenon known as dissipation trails or distrails. The heat of combustion of the jet aircraft fuel, released into the path swept by the jet, can evaporate existing clouds (if not too dense), yielding a distrail like the one shown above taken over Florida earlier this month. These linear tracks are actually the counterparts of contrails (condensation trails). Whereas contrails require very cold temperatures, at least -40 C, to form, distrails may form in relatively warm, low clouds that consist of water droplets or in thin supercooled middle or high clouds. Note also the waning gibbous Moon.

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