In a very detailed article, Andrew Johnson recounts his attempt to correlate the frequency of air traffic over various parts of the UK with the frequency of persistent contrails observed in those locations.
http://www.checktheevidence.co.uk/c..._content&task=view&id=393&Itemid=50#_ftnref20
Contrails persist in regions of air that are ice-supersaturated. Regions of ice-supersaturated air (sometimes referred to as Ice Super-Saturated Regions, or ISSR) are essentially invisible clouds. The plane passing through them makes them visible by temporarily raising the humidity. ISSRs vary in almost exactly the same way that clouds vary. So just like the sky can one day be clear, and the next day be cloudy, you can also have one day with no ISSRs, and the next day with lots, or a few broken ones (giving broken persistent contrails). And like clouds, ISSRs occur in layers, so planes flying at slightly different altitudes leave very different contrails.
None of this should be controversial. It's backed by science and observation dating as far back as the first observations of persistent contrails in the 1920s, and by discussions about contrails in over 70 years worth of weather books:
And this has been well discussed in the scientific literature for a similar length of time:
http://www.pa.op.dlr.de/issr/Cha1.html
http://www.checktheevidence.co.uk/c..._content&task=view&id=393&Itemid=50#_ftnref20
After much analysis, the conclusion of the report was what you would expect:This research used a collection of software and hardware to receive and decode ADS-B messages from aircraft as well as photograph the sky at 1-minute intervals. The software ran on several Raspberry Pi computers stationed at up to 6 different locations in the UK. The objective was to count the number of aircraft detected at a given location and compare these counts, both on an hourly and a daily basis, when the skies were clear enough to have seen persistent jet trails or “chemtrails”. Time-stamped time-lapse videos were generated for images taken between sunrise and sunset each day. These were inspected to count the number of trails observed in each 30-min period of daylight. Trail counts and aircraft counts were collated into a Microsoft Access Database. SQL Queries were then developed to allow comparison of aircraft counts during periods when trails were observed and clear periods when no trails were observed.
While there are various methodological objections that could be raised about this study, the primary problem is the ignoring of what 100 years of science tells us is the reason for persistent contrails: the weather.From all the data gathered so far, it seems there is no large difference in “ADS-B detectable” aircraft on days of high trailing than there are on days of no trailing. The data here does not establish a clear link between levels of aircraft and levels of trailing.
Contrails persist in regions of air that are ice-supersaturated. Regions of ice-supersaturated air (sometimes referred to as Ice Super-Saturated Regions, or ISSR) are essentially invisible clouds. The plane passing through them makes them visible by temporarily raising the humidity. ISSRs vary in almost exactly the same way that clouds vary. So just like the sky can one day be clear, and the next day be cloudy, you can also have one day with no ISSRs, and the next day with lots, or a few broken ones (giving broken persistent contrails). And like clouds, ISSRs occur in layers, so planes flying at slightly different altitudes leave very different contrails.
None of this should be controversial. It's backed by science and observation dating as far back as the first observations of persistent contrails in the 1920s, and by discussions about contrails in over 70 years worth of weather books:
And this has been well discussed in the scientific literature for a similar length of time:
http://www.pa.op.dlr.de/issr/Cha1.html
So while I applaud Andrew's hard work, and the database created might even have some interesting data in it, it seems like he was looking at the wrong thing. Nobody had ever claimed that days with more contrails were the result of more air traffic. It's always been about the weather, at 28,000 to 40,000 feet.The existence of cloud free air masses in the state of supersaturation with respect to ice was proven almost 60 years ago. E. Glückauf (1945) found from hygrometer data obtained over southern England that (very high) supersaturation with respect to ice occurs very frequently in the upper troposphere. H.Weickmann concluded in his 1945 review paper on "Shapes and formation of atmospheric ice crystals" (Weickmann 1945) that ice crystals in the atmosphere, i.e. cirrus clouds, form mainly via the water phase and not as soon as ice saturation is reached. He characterized the ice forming regions in the upper troposphere and the (lowermost) stratosphere as regions of high ice-supersaturation but with small absolute humidity.
...
A good marker of ISSRs is persistent condensation trails (contrails) when the sky is otherwise free of clouds. Since the mixing process in an aircraft exhaust plume can create very high degrees of supersaturation even in dry ambient air, the formation of contrails does not require as high ambient humidity as the formation of natural cirrus. Contrails can therefore decorate the sky when no cirrus clouds are around. Contrail persistence however requires at least ice saturation. A sky full of contrails but without cirrus therefore shows that there must be an ISSR.
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