Contrail Formation and Persistence

Source: http://www.chemtrailcentral.com/report.shtml

Jet aircraft leave behind a heated mixture of water, carbon dioxide, nitrogen oxides, sulfates, unburnt hydrocarbons, soot, etc. as by-products of the combustion of fuel in the engines. Water and particulates play a fundamental role as the basic foundation for the formation of a contrail. Pre-existing particles in the air will serve as nucleating bodies for the warm water to condense around, creating larger droplets that will quickly freeze given the appropriate atmospheric conditions. Fresh soot from the exhaust is generally hydrophobic, but over time can become hydrophilic, and thus suitable as condensation nuclei. The ability of the resultant ice crystals to last is governed by the ambient moisture at flight altitude. So, temperature serves generally as a threshold mechanism for the production of contrails and increased moisture provides slower sublimation rates and thus longer dissipation times for contrails. (Evaporation, often incorrectly applied to the process of contrail dissipation, is the process of a liquid changing to vapor. Sublimation is the process of a solid changing to vapor, bypassing the liquid state.) Various numbers are quoted as the threshold temperature for contrail formation: -40C, -38C, -35C. In this study, the warmest temperature at which a contrail was observed was -41C. In practice, the speed of dissipation of a contrail can be from a few seconds to hours. This varies with differing atmospheric conditions due to seasonal, daily, and frontal weather changes as well as global placement as varying local temperatures and humidity at flight levels provide differing ranges of persistence. The observations made in this report are all from Houston, TX. The conditions that support contrail formation are present, but not in an overabundance. In this study, the longest-persisting contrail observed from a known identified aircraft was approximately 25 minutes. This occurred on one occasion, out of 53 documented observations. The next longest in persistence were trails lasting approximately 2 minutes. This occurred on about 5 occasions. Most contrails observed were in the 5-20 second range. Unidentified flights were observed to produce trails with persistence from 20 seconds to several hours.

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Contrails are human-induced clouds that only form at very high altitudes (usually above 8 km) where the air is extremely cold (less than -40°C). If the air is very dry, they do not form behind the plane. If the air is somewhat moist, a contrail will form immediately behind the aircraft and make a bright white line that lasts for a short while. Persistent contrails form immediately behind the airplane in very moist air. These long-lived contrails will usually grow wider and fuzzier as time passes. http://asd-www.larc.nasa.gov/SCOOL/contrails.html

Please note: Powell River must have the most stable weather conditions on earth. Why is because everyday for at least two years solid, we have had trails hanging in the sky all over the place. They come from "every" direction.