Bruce From United States, joined May 1999, 4953 posts, RR: 28 Posted (6 years 11 months 1 day 19 hours ago) and read 1167 times:
How come sometimes I do not see contrails in the sky and other times i do. i always thought that the colder the air is, the more likely to see it since all it is is frozen vapor from the exhaust. But, sometimes on a cold day i have not seen them. is it more likely to see contrails in winter months? Many times in summer the upper atmosphere can be very cold (thats why we get hail!) but I dont always see it.
bruce
Bruce Leibowitz - Green Bay, WI (GRB/KGRB) - Canon 20D/100-400L IS lens
Prebennorholm From Denmark, joined Mar 2000, 5147 posts, RR: 55 Reply 2, posted (6 years 11 months 1 day 19 hours ago) and read 1131 times:
On a day with humid air at altitude you may see thick contrails stretching from one horizon to the other.
On a dry day you may see thin contrails which evaporate one or two miles behind the plane. Or hardly any contrails at all.
You may use that for your own weather forecast. When contrails are short, then you are most likely near the center of a high pressure area, and you may enjoy bright sunshine for the next few days at least. And visa versa.
Regards, Preben Norholm
Always keep your number of landings equal to your number of take-offs, Preben Norholm
Donder10 From Canada, joined Oct 2001, 6657 posts, RR: 30 Reply 3, posted (6 years 11 months 17 hours ago) and read 1068 times:
I was about to ask this question myself given the crazy amount of overflights we get here.
It depends on when the government decides to spray mind controlling vapors. That website says so,so it must be right!
Bio15 From Colombia, joined Mar 2001, 1052 posts, RR: 10 Reply 4, posted (6 years 10 months 4 weeks 1 day 22 hours ago) and read 1022 times:
Hi guys, I've never thought of this question: Condensation forms when the temperature decreases below the dew point, right? I assume dew points are very low up there at FLs, but why does the condensation appear when the aircraft goes by, if what is does is warm up the air?
Klaus From Germany, joined Jul 2001, 17776 posts, RR: 62 Reply 5, posted (6 years 10 months 4 weeks 1 day 21 hours ago) and read 1013 times:
Bio15: Hi guys, I've never thought of this question: Condensation forms when the temperature decreases below the dew point, right? I assume dew points are very low up there at FLs, but why does the condensation appear when the aircraft goes by, if what is does is warm up the air?
Combustion of petroleum-based fuels doesn´t just produce CO2; A significant portion of the generated energy comes from burning the hydrogen that´s chemically bound in the fuel (crude oil contains about 10-14% hydrogen).
The result of hydrogen combustion is water (vapour). Which can increase the vapour saturation in the air beyond the current dew point which in turn leads to condensation: contrails.
The actual contrail itself is made up of water, which is produced through the oxidation of hydrocarbon fuels, wherein atmospheric oxygen combines with hydrogen to form water vapor as in the following:
If temperatures are low enough, generally below -38C, the contrail will form into a linear shaped cloud of ice crystals at which time it will behave almost identically to other cirrus clouds, which are also composed of ice crystals.
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From United States, joined May 1999, 4953 posts, 
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