Clouds formed when they should not?

captfitch

Senior Member.
It looks like you're suspicious of clouds that exist at the lower levels and as are reported on the 6:51 observation but are absent on the 6:56. And that you believe the trails are there despite the observation of clouds at 25000.

You do know that those are stripped off the metar from some reporting station (in this case probably JFK)? And those metars are generated from AWOS stations? And that the JFK version has the ability to see very high clouds. Further, it updates often and could sense the lower and upper clouds as they rolled over.

Besides, those stations are all run by the FAA. So why would you trust what it says?
 

Ross Marsden

Senior Member.
In cloud reporting (or forecasting for aviation), for each identifiable cloud layer, the cloud base is given, as well as the amount.
The height is usually in feet above station.
The amount is given as FEW, SCT, BKN or OVC; for few, scattered, broken and overcast.
FEW means 1 or 2 eighths of the sky covered by that layer wich has its base at the stated height.
SCT means 3 or 4 eighths of the sky covered.
BKN means 5, 6 or 7 eighths of the sky covered.
OVC means 8 eighths of the sky covered - that is, complete cover.

My point is that the cloud base is given that there will be cloud extending from that height through the depth of that cloud layer.

H2meloen, I don't fully get the assertion either. Where were the photos taken? When in relation to the weather observations? The photos do not seem incompatible with the observations assuming they relate to the same place and time (which is what you are implying).
 

Mick West

Administrator
Staff member
Cloud not forming does not mean clouds cannot persist.

A cloud needs 100% RH to form, but only about 60-70% RH to persist as ice. That's why you ken get contrails persisting in a clear blue sky. The jet temporarily raises the local humidity so a cloud can form (where natural clouds cannot), and then it persists (as would a natural cloud)
 

solrey

Senior Member.
There can be no trails because the weather says clouds to 25,000ft only. No trails should spread into clouds or persist for any length of time.

That's not true because you're only looking at a small snippet of available meteorological information. Radiosonde data indicates that clouds and contrails could exist above 25,000 ft. on either of those days.

Following are Stuve diagrams, the line on the left is dew point, the one on the right is temperature. The closer the dew point and temp lines are together, the higher the relative humidity.

Radiosonde data for Sep. 10 from near the same local time and location.



Text file:
http://weather.uwyo.edu/cgi-bin/sou...AR=2014&MONTH=09&FROM=1100&TO=1100&STNM=72501

Radiosonde data for Sep. 4 from near the same local time and location.



Text file:
http://weather.uwyo.edu/cgi-bin/sou...AR=2014&MONTH=09&FROM=0500&TO=0500&STNM=72501
 

deirdre

Senior Member.
There can be no trails because the weather says clouds to 25,000ft only
apparently there can. you have a picture to prove it.

your second pic, note how the contrail (ice chrystals) reflects the sunset the EXACT same way as the surrounding clouds (also made of ice chyrstals). If the trail was made by some 'chemical', it would never match so exact.
 

WeedWhacker

Senior Member
The assertions in thread deserve another bit of explanation.

Essentially, the claim is that clouds "can't" form about 25,000 feet? It's because the thread OP saw one aviation weather report indicating the cloud ceiling for that observation, of 25,000 feet. In aviation weather, when the "ceiling" height of clouds is mentioned...then, there is no additional info about any other clouds that may be present, at higher altitudes.

Another example: Say you have a low overcast layer of stratus clouds.....if that aviation weather report says they're at 1,000 feet as a "ceiling"? Then, all the rest of any clouds that may be up there (and above that lowest "ceiling") are not mentioned.
 

deirdre

Senior Member.
The assertions in thread deserve another bit of explanation.

Essentially, the claim is that clouds "can't" form about 25,000 feet? It's because the thread OP saw one aviation weather report indicating the cloud ceiling for that observation, of 25,000 feet. In aviation weather, when the "ceiling" height of clouds is mentioned...then, there is no additional info about any other clouds that may be present, at higher altitudes.

Another example: Say you have a low overcast layer of stratus clouds.....if that aviation weather report says they're at 1,000 feet as a "ceiling"? Then, all the rest of any clouds that may be up there (and above that lowest "ceiling") are not mentioned.

cool. that's useful to know, what exactly a 'cloud ceiling' is.
 

WeedWhacker

Senior Member
cool. that's useful to know, what exactly a 'cloud ceiling' is.

Exactly....which is why I mentioned it, knowing that not all in the reading audience are familiar with some of these terms and definitions.

When one has training and background in aviation, then one interprets differently than (say) the layperson. Including factual info helps greatly, to prevent when possible, misinterpretation.
 

H2meloen

New Member
Thank you for the answers. What is your opinions on this one
It is from Camborne 07.08.2014 it contains more data. You can see it clearly..
There can be no ¨Persistant Trails¨ occur as you can see in the picture and the available data.

https://www.facebook.com/len.duggan.1/media_set?set=a.10152806604474954.1073741845.549534953&type=1

*Pictures of Camborne on 07.08.2014






------------------------------------------------------------------------------------------------------------------------------------


*This is the definition of the MINTRA line (minimum trail line).
It was investigated during WW2 because the white line behind the aeroplane would have meant death to the pilot from enemy fire.
Top scientists discovered this relationship between pressure, temperature and humidity.
The link below is a 1996 updated investigation into the Appleman study that discovered the MINTRA line.
http://journals.ametsoc.org/doi/pdf/10.1175/1520-0450(1997)036<1725:COACFC>2.0.CO;2


-----------------------------------------------------------------------------------------------------------------------------------


*Here is a frost point at 8,300 meters and cloud could occur from the freezing of the water vapor into ice crystals if it was cold enough..
If the humidity line met the temperature line then you would get clouds and rain.



------------------------------------------------------------------------------------------------------------------------------------


*You can get clouds here. Maybe morning dew at ground level or ground frost if it is clod enough and cloud or rain at 4,000 meters in Upton US on 11th sept 2014


--------------------------------------------------------------------------------------------------------------------------------


*Here is the height that trails might occur but not persistently (non persistent trails)..
Between 10,200 and 12,000 metes


-----------------------------------------------------------------------------------------------------------------------------------


*Here is the height that trails will persistently occur.
"Persistant Trails" is the biggest con in the understanding of trails.
Between 10,600 and 11,900 trails will occur persistently.
This has nothing to do with how long they will last in the sky.
The length of time they lasted was never investigated.
We can see that no frost point exists between these heights as the thin line does not meet the other temperature line on the right. No clouds will form from ice nucleation of water vapour.


------------------------------------------------------------------------------------------------------------------------------------


*Then we get the data in list form and check the humidity between the heights that are cold enough to make trails.
We can see that there is a maximum of only 31%RH at 11342 meters.
This means that the trails would have dispersed quickly as the water from the plane exhaust would have dissipated in the dry air.
The trails would definitely not spread out into clouds.
http://weather.uwyo.edu/cgi-bin/sounding?region=europe&TYPE=TEXT:LIST&YEAR=2014&MONTH=08&FROM=0712&TO=0712&STNM=03808




https://www.facebook.com/len.duggan.1/media_set?set=a.10152806604474954.1073741845.549534953&type=1
 
Last edited by a moderator:

JFDee

Senior Member.
There can be no ¨Persistant Trails¨ occur as you can see in the picture and the available data
Three points:

1. The radiosonde data shows humidity levels with respect to water. The factor that is relevant for persistent contrail formation is supersaturation with respect to ice - this can occur at water humidity levels below 70 %.

2. Humidity data from radiosondes at low temperatures (high altitudes) tends to be unreliable.

3. Radiosonde probing gives you one vertical snapshot at an area with tiny horizontal extension. As the distribution of clouds shows, you can get totally different values several meters away.

In a nutshell: it's not possible to predict the likeliness for contrail formation with accuracy.
 
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Hama Neggs

Senior Member.
There can be no ¨Persistant Trails¨ occur as you can see in the picture and the available data.

OK.

!)Then what is your alternate explanation as to what caused that trail?

2) What do you suppose is the mass of the material contained in that trail and where did it come from?
 

Mick West

Administrator
Staff member

Although when I analyzed the variouse stations, Camborne did actually seem to be more reliable than the other stations in actually predicting contrail formation at the same rate as expected.

The one station in England seems to be good:

Code:
2011 Camborne 03808
Jan ****************
Feb ***************
Mar ***********
Apr *************
May **********
Jun *********
Jul **********
Aug *****************
Sep *******************
Oct ******************
Nov ****************************
Dec ******************************
All contrails/soundings = 196/728 -> 26%
00Z contrails/soundings = 171/362 -> 47%
12Z contrails/soundings = 24/364 -> 6%

The ******s next to a month are the number of days that have contrail conditions. 00Z in the UK is midnight, 12Z is noon. Most contrails in the UK will occur in the AM, based on this.

I shall have to revive this code to look at the latest data.
 

WeedWhacker

Senior Member
Radiosonde data, while useful, is not exact. Nor is it comprehensive.

Keep in mind, please, that as the balloon ascends, it is drifting with the prevailing winds aloft. IOW, it is released from a specific point on the ground, but each time of release will have a variable path as the balloon ascends...because of winds.

There are other sources of data RE: atmospheric conditions besides the radiosonde balloons. Airplanes, and 'PIREPS' as requested by ATC.

ALL of these data can be "merged"....but, meanwhile the atmosphere is a continuous "living thing"...constantly changing.
 

Mick West

Administrator
Staff member
This photo:

Was taken approximately from here:
https://www.google.com/maps/@50.212...ata=!3m4!1e1!3m2!1sYSuZWS4G-_P_b42_J1ljTg!2e0


Looking about due north. Overlaying 5 mile spaced concentric circles at 11,000 meters:


Roughly shows the contrail is about 20 miles away. Even if you had a precise measurement of the humidity overhead, then 20 miles away it could be very different.

Adding a trail at 11,000m:


gives:


And looking at that photo again, you can see the humidity is very variable in the visible sky, as the cirrus layers are not solid, and the contrail is visible or not in a similar manner.
 

solrey

Senior Member.
Based on the shadows in the photo that Mick analyzed, it appears to be late in the afternoon, many hours after the 12Z readings. Below are the 12Z readings for Valentia Observatory , NW of Camborne indicating conditions favorable for contrails in the range of cruising altitudes.



http://weather.uwyo.edu/cgi-bin/sou...AR=2014&MONTH=08&FROM=0712&TO=0712&STNM=03953

Camborne and surrounding stations show favorable contrail conditions on the next sounding at 00Z 08/08/14.



http://weather.uwyo.edu/cgi-bin/sou...AR=2014&MONTH=08&FROM=0800&TO=0800&STNM=03808



http://weather.uwyo.edu/cgi-bin/sou...AR=2014&MONTH=08&FROM=0800&TO=0800&STNM=03354



http://weather.uwyo.edu/cgi-bin/sou...AR=2014&MONTH=08&FROM=0800&TO=0800&STNM=03882

All of which indicate that favorable contrail conditions moved into the area on westerly winds later in the afternoon.
 

skephu

Senior Member.
I'm looking for a pdf of this seminal paper but can't seem to find it on the web:
Appleman H., 1953: The formation of exhaust condensation trails by jet aircraft. Bull. Amer. Meteor. Soc, 34, 14–20.
I would be grateful if someone could send me the pdf.
 

deirdre

Senior Member.
Me too, but that's only the first page. The paper is 7 pages.
it seems to be used as a reference quite a bit. youd think it would be online somewhere.

edit: do you know the name of the 'paper' it is embedded in? its on page 14 of something it appears ?
 

Mick West

Administrator
Staff member
it seems to be used as a reference quite a bit. youd think it would be online somewhere.

edit: do you know the name of the 'paper' it is embedded in? its on page 14 of something it appears ?

Bulletin of the american meteorological society, 1953, Issue 34
 

deirdre

Senior Member.
I guess im thinking if we can figure out what the other contents are it might be online listed as one of the other articles. but I cant see this pic good (from ebooks) am I making sense?

books.jpg

probably not .sorry. its pretty long apparently, who want to scan all that
S. E. Reynolds, "Thunderstorm-precipitation growth and electrical-charge generation," Bulletin of the American Meteorological Society, vol. 34, pp. 117–123, 1953.
 
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