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The goal of this research was to determine if there was a type of trail that was inconsistent with normal contrails, especially with regard to increased persistence. What was found is that highly persistent trails that last for many hours were seen above Houston, TX on a majority (60%) of observable days during the data collection period. However during this time period none of the 46 Flight Explorer confirmed contrails observed persisted for over 30 minutes and most contrails were under 30 seconds of persistence. Additionally it was discovered that the jets that were responsible for leaving highly persistent trails that last for hours did not ever appear on Flight Explorer and were documented for 8 separate instances, including one instance with two jets in formation. These unidentifiable jets were found to produce a contrail that was consistent with confirmed contrails during the periods when they weren't leaving highly persistent trails. Highly persistent trails are often seen in the form of isolated relatively short strips, as well as large areas of cirrus aviaticus clouds, but on rare occasions have been seen in totally unique grid and wheel formations.

It is hoped that others will endeavor to repeat these observations and publish their results. By repeating the basic observations for persistence length and whether the flight appears on Flight Explorer, it will be seen whether or not a trend emerges confirming the existence of a unique category of trail. Atmospheric differences due to higher moisture and colder temperatures in different locations will produce greater maximum persistence observed for identifiable traffic. For those in locations with greatest contrailing potential, the task of collecting data on highly persistent trails from unidentifiable flights will be hardest.

In this research I have gone to great lengths to measure and characterize my observations as accurately as possible in order to provide the clearest representation possible given the resources available.

M Steadham