Martin

I think I took that to mean that vapour trails contrails don't exist (these days).</I>

Yes, easy to have misunderstood actually. I just meant that modern technology as well as the buyers of aircraft demand that everything be done to minimize any waste from engine exhaust. If that amount of smoke came out of an engine most knowledgeable people would think the plane was on fire and call 911. Instead, today people can't even be bothered to look up.

@Martin A Mar 8, 2014 at 1:14 PM

And btw, with the high sun behind and to one side of the aircraft you can often see the shadow of the contrail on the ground opposite. The thin dark line looks quite puzzling till you twig.

Yes, in absolute terms. But I think it is the relative humidity that counts.

What counts depends on what meaning is inyended.

http://en.wikipedia.org/wiki/Relative_humidity

Misconception

The notion of air holding water vapor is sometimes used to describe the concept of relative humidity. This, however, is a misconception. Air is a mixture of gases (nitrogen, oxygen, argon, water vapor, and other gases) and as such the constituents of the mixture simply act as a transporter of water vapor but are not a holder of it.

Relative Humidity is defined in the physical properties of water and thus is unrelated to the notion of air holding water.

I am meaning that the air at 30,000' and -30 can be described as having 'low humidity' by any standards. Because this air has 'low humidity' a garden variety 'vapour trail' (condensation trail) will dissipate in seconds.

http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/relhum.html

Relative humidity is the amount of moisture in the air compared to what the air can "hold" at that temperature. When the air can't "hold" all the moisture, then it condenses as dew.

I certainly may be describing this incorrectly. As I am only a layman and scientific terms most certainly contain ambiguity for me rather than specific concepts as they are intended. Still, the air at 30,000 feet and at -30 is I think always described in human terms, and also in human machine terms, as dry. Very dry.

In other words -

The air at sea level can conceivably have a lower relative humidity than air at a higher altitude yet still the air at sea level feels moist and the air at altitude is dry. Why? Because of the amount of moisture in the air is much, much less. There is very little. It feels very dry to the skin. That would be my interpretation.

But it could be wrong, I have never been at sea level and then at a higher altitude and witnessed a lower relative humidity and subsequently a higher relative humidity so that is only my layman's interpretation. Still, I will stick with the claim that the air at 30,000 feet and -30 is dry. I believe it has a low relative humidity, extremely low by human standards. I believe if this wasn't the case and it had a high relative then ice would form on planes. And in fact we know that this is an extreme danger for pilots and is to be avoided at all costs.

"presumably early flights from Heathrow, Schiphol or CDG heading for Asia."

Why presumably when you can check? If you actually wanted to check rather than presume you could use this tool. You can use it two ways. You can check what flight it is when you see a trail. You can check on a scheduled flight that you know and see if it creates a trail.

http://www.flightradar24.com

it's relative humidity that is the important factor in their creation and the winds aloft that determine how long they persist.

Relative humidity can explain condensation trails. But anything that you see that persists longer than a minute is not a condensation. Trails that last for hours and disperse into stringy convoluted shapes are not condensation trails.

Actually a minute is most likely on the long side for contrails.

Actually I left out the most important part. A regularly scheduled flight, or a charter flight I believe, will only produce a garden variety condensation trail that dissipates within a few seconds. Flights that you see producing long plumes of whitish product will not show up on flightradar. Why? Because they aren't passenger carriers. They are there for the only purpose of dispersing whatever it is they are dispersing.

"But I'm afraid I am not about to fire up my computer at 7am just to check and see if what I believe to be a long haul from western Europe to the Far East is in fact so.
That would be a bit anal-retentive, don't you think?

Well I guess it depends on how interested you are. To somebody who is very interested in something such an activity would be insignificant.

all the information I can get on chemtrails tells me they are figments of conspiracy theorists' fevered imaginations.

Well if that's all the information you can find there isn't a whole lot of much I can do. All information is available. Those who seek God find God. If you don't believe in God you find reasons for that. If you believe Maurice Strong and the Club of Rome wants to decimate the population as apparently posters on this site believe, then you find proof of that. If I were to post a link you would only come back with a snicker and tell me that has been debunked. You must use your own reason and do your own research and diligence. Otherwise it matters not.

I am presenting these reasons as I have as an exercise for myself to understand. To me it is not worthwhile to post on sites where people repeat after me - Yea, good one man. Here's another. Such posting lacks juice.

What I'm trying to say is that you ask for facts that you want to check but this is in my opinion an incorrect starting point. Pointless actually. You must first have reason to check the facts. In my case I have reason to believe chemtrails exist because my reason tells me those are not contrails so I pursue the facts and I believe I find them. So I present 'my facts'. My reason tells me it is a bad idea to pump toxic liquid into ground water so I pursue the facts. And I believe I find them. People think it is the other way around but I would disagree. People think you find facts first. I disagree. And of course it builds upon itself. Nevertheless, it is my belief that reason creates the path. In my path to justify my reason I search the internet, but it is irrelevant to present links to other sites which I would agree with. They are not proof to you or to anybody else. Only your reason can provide you that proof.

I think my reasoning is better than your reasoning. :)

Martin A
Replicant says that aircraft vapour trails do not exist. Or at best, they last just a few seconds. And this is scientifically proven. What we see are *chemtrails* - whose nature is not known but is probably sinister. [replicant - have I correctly described your view?]

Perfectly. With some slight adjustment. Extend the time frame for the existence of the condensation trail somewhat depending on what your concept of what 'a few seconds' is. The concept of 'do not exist' and 'preclude' is because of the construction of a modern jet engine which came about called a hi bypass turbofan engine. These are fitted with the large rotary blade and gather a larger amount of air than that which is needed for combustion and force it past the engine itself to make it a part of the thrust, after the combustion. Increasing thrust while minimally increasing combustion. Thus the exhaust is already mixed with clean air before becoming thrust. Or I imagine, at the same time. This type of engine minimizes the formation of condensation trails greatly. If you took away all the chemtrails you would hardly see much contrail activity from todays air traffic.

TThere is absolute humidity and there is relative humidity. Absolute humidity is the total quantity of water vapour in the air; relative humidity is the amount of water that the air can hold as a vapour, and is usually expressed as a percentage – i.e. 100% humidity is when the air cannot hold any more water, the dew point is reached, and the water condenses; however, if the temperature is low, the absolute humidity can be very low, while the relative humidity can be very high. This is how clouds, mist, fog and contrails are formed. The absolute humidity at altitude may be very low, but the relative humidity can be high, thus, any extra water vapour introduced condenses and forms a cloud. If the source of the water is fast-moving, such as an aircraft, then that cloud will be extended behind the source, appearing as a contrail. The relative humidity (RH) of the air in that locale will dictate the time-span of visibility of the contrail; the various winds at those altitudes will also have some effect upon life-span, dissipating the condensed water over larger volumes of lower-humidity air (which is why contrails can be seen to bend and shear, and often may streak out laterally, similar to cirrus clouds).

Stratification of the atmosphere can cause layers of differing RH to exist, so clouds form at varying heights, and a contrail can appear and disappear as an aircraft climbs after take-off.

Replicant, based upon the many conflicts in your arguments, I suspect that this “previous life” when you were a nuclear scientist was actually a previous life, you being a believer in reincarnation.

Replicant, based upon the many conflicts in your arguments

What conflicts in my arguments?

I was rereading thread and my earlier posting and I have to say I'm not proud of a lot of it. I'm a pretty big cynic and I come with some preconceived notions. Which are not the same as my arguments. So I just wanted to take a moment to apologize to the blog and especially to Martin A for the past attitude I presented.

Well said rep. You are bigger than me.
So far I've never made a mistake that I couldn't blame on somebody else.

Yes indeed that is me. No one would dare pass themselves off as me. Too easy to be exposed. :) Sincerely.