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Persistent Contrails


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Posted
  • Location: South Woodham Ferrers, height 15 metres
  • Location: South Woodham Ferrers, height 15 metres

Hi, I've just been walking outside. Beautiful clear blue skies, and the few airplanes there are in it are like comets, shooting across the sky with short white contrails behind them. This is different to yesterday. Sunday the jets were leaving persistent contrails. Sunday was a pretty good day like today. What is the difference that explains the short contrails we have today and the ones that covered the entire sky yesterday?

The difference may have something to do with temperature and humidity.

What charts can I look at which show this so I can predict which days will have short and long contrails ... and by extension, by looking at contrails alone be able to know what the temperature/humidity is like at certain heights in the atmosphere.

You can track the heights of the contrails using flightradar.

http://www.flightradar24.com/

Any help answering this question and links appreciated.

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Posted
  • Location: South Woodham Ferrers, height 15 metres
  • Location: South Woodham Ferrers, height 15 metres

I'll periodically return to this thread, so if you've only just read it and it's about two weeks after I've posted it, I'm still interested. I'll post here with an update as soon as I find the information elsewhere.

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Posted
  • Location: South Woodham Ferrers, height 15 metres
  • Location: South Woodham Ferrers, height 15 metres

Skew-T charts could be useful. Could work out approximate height from mb while dew point provides a measure of humidity - if I read the chart correctly.

According to this.

600mb = 14,000 feet

400mb = 25,000 feet

250mb = 36,000 feet

150mb = 46,000 feet

So this chart of 12pm today when there were short contrails suggests... judging by 500mb - 400mb level (20-25,000 feet), dewpoint was between -10C and -17C (the lower side). Presumably on Sunday the dewpoint was higher, so the water vapour from the jets did not have to cool so much to condense, because the contrails on that day were persistent. I don't know this though because I don't have skew-T plot from Sunday. I'll have to check another day to see if this works.

2hs94p3.png

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Posted
  • Location: South Woodham Ferrers, height 15 metres
  • Location: South Woodham Ferrers, height 15 metres

Clear blue skies again today.

Just had an Air Berlin fly overhead at 36,000 feet. That's higher than most of the high planes which are usually somewhere over 20k. As it passed over it left a pretty good contrail that extended all the way across the sky. However, 15 minutes later it's virtually all gone.

At this level the air is currently about - 12C with a dew point of - 20C.

For really strong contrails we're looking for cold, humid air. This is cold enough but has very low humidity, which I'm guessing could be why the contrail was long but short duration.

4gp4wk.png

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Posted
  • Location: South Woodham Ferrers, height 15 metres
  • Location: South Woodham Ferrers, height 15 metres

Just had another fly by. It wasn't on flightradar24 but it looked about the same height. The contrail is behaving exactly the same way. Really long contrail but it's dissipating rapidly and will probably all disappear.

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Posted
  • Location: Camborne
  • Location: Camborne

Clear blue skies again today.

Just had an Air Berlin fly overhead at 36,000 feet. That's higher than most of the high planes which are usually somewhere over 20k. As it passed over it left a pretty good contrail that extended all the way across the sky. However, 15 minutes later it's virtually all gone.

At this level the air is currently about - 12C with a dew point of - 20C.

For really strong contrails we're looking for cold, humid air. This is cold enough but has very low humidity, which I'm guessing could be why the contrail was long but short duration.

4gp4wk.png

I think you might want to check your temps for 36,000ft. Basically the length of time that contrails exist is dependent on speed of sublimation which is dependant on the WV content of the air. The less WV in the air the quicker they dissipate and the reverse is true if the air is nearly saturated. If they persist they are spread by the upper winds and you can get almost complete cover the sky.. And don't forget that's a forecast diagram and won't be completely accurate. And of course you can also get distrails due to heat evaporating cloud droplets.

I take you have looked at the Netweather article on the subject? Thanks John.

http://forum.netweat...ttach_id=104770

Edited by weather ship
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Posted
  • Location: South Woodham Ferrers, height 15 metres
  • Location: South Woodham Ferrers, height 15 metres

Wow, never seen a sky with contrails like that.

I think you might want to check your temps for 36,000ft. Basically the length of time that contrails exist is dependent on speed of sublimation which is dependant on the WV content of the air. The less WV in the air the quicker they dissipate and the reverse is true if the air is nearly saturated. If they persist they are spread by the upper winds and you can get almost complete cover the sky.. And don't forget that's a forecast diagram and won't be completely accurate. And of course you can also get distrails due to heat evaporating cloud droplets.

I take you have looked at the Netweather article on the subject? Thanks John.

http://forum.netweat...ttach_id=104770

-20C dew point must be pretty low on the water vapour.

Temp at 250mb (roughly 36'000 feet according to the link I posted) looks to be -10C.

If you have any links to make these observations more accurate, please post!

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Posted
  • Location: Camborne
  • Location: Camborne

Wow, never seen a sky with contrails like that.

-20C dew point must be pretty low on the water vapour.

Temp at 250mb (roughly 36'000 feet according to the link I posted) looks to be -10C.

If you have any links to make these observations more accurate, please post!

You can't possibly have a temp of -10C at 250mb. On your diagram it's about -58C

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Posted
  • Location: South Woodham Ferrers, height 15 metres
  • Location: South Woodham Ferrers, height 15 metres

Don't you just draw a line up? The x-axis says "temperature". Unless you are saying you follow the blue line, in which case what line to you use for the dew point?

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Posted
  • Location: Camborne
  • Location: Camborne

I'm actually not quite sure what you mean. Below is todays midday Camborne ascent. The temperature lines of the diagram run diagonally left to right from the surface and are clearly marked. The environmental dew point profile is in green and the temperature in black. From this you can see that the temp at 500mb is -20C, which you can either read straight off or follow the temp diagonal down to the surface. Similarly the dew point is -34C.

JH has written asimple guide to reading Skew-T diagrams that is well worth reading apart from the link I've already posted.

http://forum.netweat...kew-t-diagrams/

Edited by weather ship
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Posted
  • Location: South Woodham Ferrers, height 15 metres
  • Location: South Woodham Ferrers, height 15 metres

Thanks for the link and the explanation. I'm not sure if I'm going to get my head around dry adiabatic lapse rates and such without actually working through examples, but it's fun, and a start, to learn how to read the temperature - and apply it. Sort of, bearing in mind these are forecasts and not highly accurate.

Monday 400-500mb - short / dissipating contrails

Temp: -25°C

Dew Point: -41°C

http://i42.tinypic.com/2hs94p3.png

Tuesday 250mb - long / dissipating contrails

Temp: -58°C

Dew Point: -65°C

http://i42.tinypic.com/4gp4wk.png

Don't know what to make of that yet... need some more observations. Eventually the errors may even out and a pattern may emerge.

Edited by AtlanticFlamethrower
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  • 3 weeks later...
Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

I've only just noticed this AF and WS-the item in which I explain how forecasters predict when contrails will occur and also enable them to differentiate between persistent and non-persistent is in the Guides section, see link below; if you are still not clear about how its done please pm me and I'll try to help

jh

http://forum.netweather.tv/topic/41377-contrails-what-are-they/

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Posted
  • Location: Camborne
  • Location: Camborne

I've only just noticed this AF and WS-the item in which I explain how forecasters predict when contrails will occur and also enable them to differentiate between persistent and non-persistent is in the Guides section, see link below; if you are still not clear about how its done please pm me and I'll try to help

jh

http://forum.netweat...-what-are-they/

That's a different link to the one I posted John. Have you got a couple of articles on the go. Anyway thanks.

http://forum.netweather.tv/index.php?app=core&module=attach&section=attach&attach_id=104770

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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

That's a different link to the one I posted John. Have you got a couple of articles on the go. Anyway thanks.

http://forum.netweat...ttach_id=104770

dunno - I lose count after 7 or 8 years on here!

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  • 3 weeks later...
Posted
  • Location: South Woodham Ferrers, height 15 metres
  • Location: South Woodham Ferrers, height 15 metres

Thanks for the replies John and WS! I'll look through the links when I get some time and the weather changes.

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