It looks like you're using an Ad Blocker.
Please white-list or disable AboveTopSecret.com in your ad-blocking tool.
Some features of ATS will be disabled while you continue to use an ad-blocker.
For a contrail to form, suitable conditions must occur immediately behind a jet engine in the expanding engine exhaust plume. A contrail will form if, as exhaust gases cool and mix with surrounding air, the humidity becomes high
enough (or, equivalently, the air temperature becomes low enough) for liquid water condensation to occur. The level of humidity reached depends on the amount of water present in the surrounding air, the temperature of the surrounding air, and the amount of water and heat emitted in the exhaust.
Atmospheric temperature and humidity at any given location undergo natural daily and seasonal variations and hence, are not always suitable for the formation of contrails. If sufficient humidity occurs in the exhaust plume, water condenses on particles to form liquid droplets. As the exhaust air
cools due to mixing with the cold local air, the newly formed droplets rapidly freeze and form ice particles that make up a contrail. Thus, the surrounding atmosphere’s conditions determine to a large extent whether or not a contrail will form after an aircraft’s passage. Because the basic processes
are very well understood, contrail formation for a given aircraft flight can be accurately predicted if atmospheric temperature and humidity conditions are known.
After the initial formation of ice, a contrail evolves in one of two ways, again depending on the surrounding atmosphere’s humidity. If the humidity is low (below the conditions for ice condensation to occur), the contrail will be short-lived. Newly formed ice particles will quickly evaporate as exhaust gases are completely mixed into the surrounding atmosphere. The resulting
line-shaped contrail will extend only a short distance behind the aircraft.
If the humidity is high (greater than that needed for ice condensation to occur), the contrail will be persistent. Newly formed ice particles will continue to grow in size by taking water from the surrounding atmosphere. The resulting line-shaped contrail extends for large distances behind an aircraft . Persistent contrails can last for hours while growing to several
kilometers in width and 200 to 400 meters in height.
Contrails spread because of air turbulence created by the passage of aircraft, differences in wind speed along the flight track, and possibly through effects of solar heating.
Originally posted by Manasseh
Are you telling me that the difference between 8000ft and 30000ft was
137f and 80% RH. Conditions for contrails to form around -45f and 80-100% RH