Curious-- how low can persistent contrails form?

Tapir-mâché

New Member
Please forgive me if I've overlooked the answer to this, but I've been lurking for a bit and something piqued my curiosity. (Also, this might belong in rambles, but I'm not able to post there yet.)

So, while I don't believe in chemtrails myself, I know one of the arguments used by believers is that they experience physical symptoms when persistent trails appear. Since the trails form high up enough that any material from them would take a long time to fall, this reaction (probably) has a secondary cause.

What I'm curious about is this: What's the lowest altitude at which a contrail can form and persist for several hours? That is, given that contrails need several conditions to show up and stick around, what's the lowest altitude where these ideal conditions would be more-or-less consistently present? I know they appear at or near ground level on occasion, but those don't really seem to last for an appreciable length of time.

Thanks, and sorry again if I missed the answer to this elsewhere!
 

Trailblazer

Moderator
Staff member
The answer is "it depends". In polar regions, persistent contrails can form at ground level.

In temperate zones (eg where I live in the UK), they are rarely seen below about 25,000 feet. But it's impossible to give a hard and fast rule because temperatures and other conditions vary so much.
 

SR1419

Senior Member.
Technically, a contrail can form at any altitude if its cold enough. Its needs to be approximately -40 for a contrail to form. Persistence is a factor of the level of humidity. Cold air holds less moisture so its relative humidity with respect to ice that allows a contrail to persist. Some cold weather airports (AK, Siberia etc..) have been known to have visibility issues due to persisting contrails at ground level. Given the variability of the atmosphere, there is no definitive altitude to assign to your question.
 

Tapir-mâché

New Member
Thank you for your replies. From what I gather, is it also not really possible to estimate higher atmospheric conditions based on local weather? Like, it wouldn't be possible to make an estimation like, "At 70 degrees Fahrenheit and 30% humidity, the lowest altitude persistent contrails would likely be able to form is..." without more data.

ETA: Or would it be possible to estimate using the presence/absence of other types of clouds?

(Meteorology' s never really been my area-- I was always better with dirt.:p)
 
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Landru

Moderator
Staff member
Thank you for your replies. From what I gather, is it also not really possible to estimate higher atmospheric conditions based on local weather? Like, it wouldn't be possible to make an estimation like, "At 70 degrees Fahrenheit and 30% humidity, the lowest altitude persistent contrails would likely be able to form is..." without more data.

ETA: Or would it be possible to estimate using the presence/absence of other types of clouds?

(Meteorology' s never really been my area-- I was always better with dirt.:p)
That is why they release weather baloons to determine conditions at higher elevations.
 

Tapir-mâché

New Member
I kind of figured, but wasn't sure.
I'd been having trouble researching this because it's (presumably) not a common query, and the results I was getting were all either explaining how contrails form at higher altitudes or expounding on geoengineering CTs. (Both of which are kind of unhelpful when you're trying to write an sci-fi weather engineering scenario without using a lot of handwaving.)
Figured I'd have a better time asking plain language questions to human people who're better versed in the subject. Thanks again!
 

deirdre

Senior Member.
Both of which are kind of unhelpful when you're trying to write an sci-fi weather engineering scenario without using a lot of handwaving.)
One thing to keep in mind is "weather" is local. "climate" is worldwide. So if you are talking about "weather engineering"
you are probably thinking of cloud seeding, not "chemtrails". or maybe HAARP or UFOs using beams to move El Nina etc.

of course in "Johnathan Strange and Mr. Norrell", John accomplished all this ^^ with witchcraft and his side won the war.

There really isnt anything fun or evil you could do with contrails.
 

Tapir-mâché

New Member
One thing to keep in mind is "weather" is local. "climate" is worldwide. So if you are talking about "weather engineering"
you are probably thinking of cloud seeding, not "chemtrails". or maybe HAARP or UFOs using beams to move El Nina etc.
It is more like cloud seeding, only actually forming clouds versus working with existing ones-- a bit more than cloud seeding as it's practiced now, but far less than climate engineering. It's a minor aspect really, but one I wanted to try to get as correct as I could. ;)
 

Mick West

Administrator
Staff member
I know they appear at or near ground level on occasion, but those don't really seem to last for an appreciable length of time
Maybe that's because nobody followed them with a camera. With just a light wind of 5mph, then in an hour the trail will be five miles away - so how would you know how long it lasted?
 

deirdre

Senior Member.
It is more like cloud seeding, only actually forming clouds versus working with existing ones-- a bit more than cloud seeding as it's practiced now, but far less than climate engineering. It's a minor aspect really, but one I wanted to try to get as correct as I could. ;)
do you have a story location in mind? That would make giving information specific to your story alot easier. For instance engine contrails dont form close to the ground in Florida.

You can try looking over http://contrailscience.com/
or when you google search a 'topic' add Metabunk to your search phrase. I have better luck on google than using the in-site search here.
 

Tapir-mâché

New Member
do you have a story location in mind? That would make giving information specific to your story alot easier. For instance engine contrails dont form close to the ground in Florida.
A temperate, Earth-like place. Not actually Earth, but close enough. I figure the area has a climate similar to the mid-Atlantic region of the U.S.

With just a light wind of 5mph, then in an hour the trail will be five miles away - so how would you know how long it lasted?
I'm just basing that off of the ones I've personally seen-- they seem to disperse comparatively quickly, though it's likely that that appearance is also a function of my proximity to them.
 

NoParty

Senior Member.
...a contrail can form and persist for several hours...
Hi. Most of these responses have to do--appropriately--with altitude, but I'm more intrigued with the highlighted part:

Are you actually seeing contrails that last more than 3 hours?

I ask because I've read a million times claims about "a chemtrail that persists and expands all day" but I
can't remember ever seeing that phenomenon once. I also haven't seen a time-lapse video of it either.
I haven't even seen a half day (in person...or a video) for that matter...or even 3 or 4 hours.

Not once. Not a single time in my life...and I'm an avid outdoorsman. Admittedly, I'm a bit ADHD
and have never chosen to stare at a particular contrail for hours...but I do have a nifty Brinno time-lapse camera,
and have done plenty of time-lapse vids...and never had a 9 or 6 or even 3 hour contrail.

My frustration is not aimed at you, Tapir-mâché, :) I just wanna find out where people are supposedly
seeing these marathon contrails...their existence is treated as a "given" by many "chemtrailers,"
and supposedly if I just "look up!" I'll realize the problem...but I'm personally having a tough time
getting outraged about all these day-long "chemtrails"...until, at least, I see my first one...
 

Tapir-mâché

New Member
Hi. Most of these responses have to do--appropriately--with altitude, but I'm more intrigued with the highlighted part:

Are you actually seeing contrails that last more than 3 hours?

I ask because I've read a million times claims about "a chemtrail that persists and expands all day" but I
can't remember ever seeing that phenomenon once. I also haven't seen a time-lapse video of it either.
I haven't even seen a half day (in person...or a video) for that matter...or even 3 or 4 hours.
Day long? No way. I've seen some that lasted maybe two or three hours (and spread more and more thinly as time progressed), but I'm inclined to think things that persist longer are just either a perspective trick or successive trails laid over each other. Of course, I wasn't plane-spotting at the time-- I can't really offer anything more definitive than "Sometimes I've been outside, and contrails were there for awhile too." Day-long trails seem like a confirmation bias thing more than anything else.

ETA: Using the word "several" was probably inaccurate, but I figured it was close enough to the longest-lived ones I've experienced.
 

deirdre

Senior Member.
only actually forming clouds versus working with existing ones
so you want to use plane like devices to make rain clouds (presumably to rain on people?)

that's gonna take ALOT of moisture! you could lower your gravity? on your planet, so air pressure is thinner at rain cloud level? thinner air has a lower saturation point. But youre still gonna have to suck alot of water from somewhere other than a plane type ship that uses regular combustion.

Sorcerers are easier.
 

Tapir-mâché

New Member
Yeah, I've got a few ideas kicking around for how the moisture problem would work... I know regular planes wouldn't really cut it, but I'm not necessarily limited to that.

so you want to use plane like devices to make rain clouds (presumably to rain on people?)
It's more an aspect of an isolated utopian spot where everything's engineered to a kind of ideal, down to the color of the grass and the puffy white clouds in the sky. Not really a huge part of the story proper, I just wanted a better grasp of some of the ways it might be engineerable before I decided if it was worth going that route.

Sorcerors would totally be easier.
 

Trailblazer

Moderator
Staff member
The problem with making rain clouds is that you'd need a heck of a lot of moisture. Contrails form cirrus clouds, which contain very little water compared to rain clouds: as can be seen by the fact that they are thin and translucent.

The air up where contrails form contains hardly any moisture, compared to the air lower down. Even if it's 100% relative humidity up there, the absolute humidity is still extremely low simply because the air is so cold and thin that it can't hold much water vapour at all.
 
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derwoodii

Senior Member.
Thank you for your replies. From what I gather, is it also not really possible to estimate higher atmospheric conditions based on local weather? Like, it wouldn't be possible to make an estimation like, "At 70 degrees Fahrenheit and 30% humidity, the lowest altitude persistent contrails would likely be able to form is..." without more data.

ETA: Or would it be possible to estimate using the presence/absence of other types of clouds?

(Meteorology' s never really been my area-- I was always better with dirt.:p)

Trailblazer uses this sites graphics http://earth.nullschool.net/ very well, perhaps he can assist you in its better use to predict winds and humidity that contribute to creation of contrail

winds.PNG

i gave it my 1st go but struggle with its depth of data,,, ( edit ops forgot no click policy, so here some pictures ) the blue blobs are areas atmosphere with higher humidity that conducive to contrail formation
http://earth.nullschool.net/#curren...tive_humidity/orthographic=-218.40,-37.57,157

windoverozhumid.PNG
here he predicts pending trail conditions over head

https://www.metabunk.org/photos-of-...t-you-took-yourself.t1487/page-20#post-178545
 
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Mick West

Administrator
Staff member
Day long? No way. I've seen some that lasted maybe two or three hours (and spread more and more thinly as time progressed), but I'm inclined to think things that persist longer are just either a perspective trick or successive trails laid over each other. Of course, I wasn't plane-spotting at the time-- I can't really offer anything more definitive than "Sometimes I've been outside, and contrails were there for awhile too." Day-long trails seem like a confirmation bias thing more than anything else.
The wind factor also comes into play here. Upper air winds can be up to 100 mph, and even at relatively low altitudes like 10-20,000 feet it can be around 50 mph quite consistently.

http://www.usairnet.com/cgi-bin/Win...AC&Submit=Get+Forecast&hour=06&course=azimuth

20160328-101115-jqmta.jpg

So in four hours, even a low altitude trail will generally be over the horizon. And old trails that are nearby will be so spread out as to be indistinguishable from clouds.
 

SR1419

Senior Member.
I ask because I've read a million times claims about "a chemtrail that persists and expands all day" but I
can't remember ever seeing that phenomenon once. I also haven't seen a time-lapse video of it either.
I haven't even seen a half day (in person...or a video) for that matter...or even 3 or 4 hours.
Most people dont watch the sky all day..and a time lapse would be difficult given the movement of the contrail with the upper winds but...studies have tracked contrails and the resulting cirrus for a very long time.

http://onlinelibrary.wiley.com/doi/10.1029/97GL03314/abstract
 

NoParty

Senior Member.
Most people dont watch the sky all day..and a time lapse would be difficult given the movement of the contrail with the upper winds but...studies have tracked contrails and the resulting cirrus for a very long time.

http://onlinelibrary.wiley.com/doi/10.1029/97GL03314/abstract
Thanks, SR. :)

Hmmm...that's interesting.

I'm still skeptical...I can't tell if these are real, normal, naturally occurring contrails they're referring to...

"The climatic impact of contrails will be greater than would be estimated if only linear contrails,
those typically observed in satellite imagery, are considered."

Also, the time lapse camera can take in a big portion of the sky...enough--in most cases--to follow the
movement of a contrail over time. I just can't figure how these all day trails are supposedly so common,
when I can't even get a single 3 hour sample...
 

Tapir-mâché

New Member
I'm not so much concerned with moisture, just the atmospheric conditions. A better way to phrase it might be, "What're the lowest, longest-lasting man-made clouds it'd be possible to form on an average spring day?"

I think I might have enough to go on now, though. :)
 

Hama Neggs

Senior Member.
I'm not so much concerned with moisture, just the atmospheric conditions. A better way to phrase it might be, "What're the lowest, longest-lasting man-made clouds it'd be possible to form on an average spring day?"

I think I might have enough to go on now, though. :)
You're wanting a definitive answer on something which is just not that quantifiable. Too many variables.
 

Tapir-mâché

New Member
You're wanting a definitive answer on something which is just not that quantifiable. Too many variables.
Which works out fine for me, really-- if it can't be easily quantified, there's probably less chance I'll be told I'm doing it wrong.

If we remove aircraft from the equation, as in the rephrased question, the answer is 500 metres - a typical altitude for the ship tracks. Also, there is a Metabunk thread about this phenomenon: https://www.metabunk.org/ship-tracks.t488/
Ship tracks. Perfect! :D I'll check it out.
 

Jay Reynolds

Senior Member.
Tapir-mache:

If you used hydrogen as fuel for the planes in your story line you would probably produce much more water in the exhaust. The amount could be calculated given the hydrogen burned. Hydrogen might be a good source of renewable 'universal' fuel for a remote planet without hydrocarbons, needing only water for a source. Fuel cells, etc. for other uses.
 

Hevach

Senior Member.
If you used hydrogen as fuel for the planes in your story line you would probably produce much more water in the exhaust. The amount could be calculated given the hydrogen burned. Hydrogen might be a good source of renewable 'universal' fuel for a remote planet without hydrocarbons, needing only water for a source. Fuel cells, etc. for other uses.
Something to remember harvesting hydrogen from water for use as a universal fuel: It takes more energy to break down the water than you get back recombining it. I've seen a few authors make this mistake, even a couple really good ones (Arthur C. Clarke, for example, in one of his books had water powered cars where you just topped up the fuel cells with distilled water every few days and they produced their own hydrogen fuel, then burned it for locomotion). Cracked water fuel cells make a great mobile fuel source, but thermodynamics makes them not work as a primary source.

However, since you're already cracking hydrogen, fusion can yield an immense energy profit, especially if you can fuse heavier elements and not just hydrogen-to-helium. It would be able to power the planet, crack water for its own fuel, and produce surplus hydrogen for fuel cells, since not everything can run off fusion (vehicles, for example).

Another option is an environmental system as the primary energy source (geothermal, tidal, wind, solar, biological), again using that energy to crack water for use as a mobile fuel source.

In both cases the process of cracking water and then burning the hydrogen is a net loss of energy because of thermodynamics, but this is true of mobile electricity sources in general - you get less watt-hours back out of a battery than you use to charge it, for example. The necessity of certain applications being internally powered and not grid powered means you have to accept a degree of inefficiency, producing surplus energy in the grid to fuel these systems.
 
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