Persistent Cumuliform Contrails at 25,000 feet over California?

Mick West

Administrator
Staff member
Very interesting skies today, halos, circumhorizon arc, other arcs, ripples, various layers of cloud.

This one caught my eye because it had a dramatic looking bend in it.

Taken at 00:42 May 29 2015 (today is the 28th, but in UTC it was the 29th), near Bullard, CA. Looking north.

The bend can be explained by perspective, and has been seen many times before, so I thought I'd look it up as an example. But it turned out a bit more interesting. The only candidate was a turboprop at 25,000 feet:
http://www.flightradar24.com/2015-05-29/00:28/12x/N407QX/660c33b

N407QX, QXE555 PDX to FAT (Portland to Fresno)

Not only that, but it went horizon to horizon. (the curve here is due to the panorama perspective. Both sections were perfectly straight, as in the FR24 track)


It also seems to be far more puffy than normal contrails, very similar to the cumulus-like clouds around it.

About five minutes later the trail had moved, seemingly with the clouds.


This was something else, illustrative of the atmosphere:


Then, later that day, nearby in Cameron Park, Looking NW I saw:

0127:14 UTC, May 29

Which, 7.5 minutes later, became (iPhone photos):

0134:41 UTC

Again, the culprits seemed obvious, again, they were at around 25,000 feet, but very different planes.


SAS963, an airbus A340, and VIR20V, a 747-400, two very large planes.

Then it looked like this, what seems to be a Circumzenithal arc, indicating it's made of ice.

0137:27 UTC


Here's a link to the full sized image of the trails forming:
https://www.metabunk.org/sk/IMG_5595.JPG

So, what exactly is going on? Persistent cirrocumulus contrails at 25,000 feet?

More photos tomorrow, I just wanted to get a first pass at it up so others can look at it overnight.
 

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deirdre

Senior Member.
well according to this site
and if a rough estimate is 5 degrees for every 1000 feet. to be -40 then the ground would be round about 85 degrees. and thats not accounting for the cumulous which kinda act like ice cubes in your soda :)

the only reason contrails dont persist once they form, is because they evaporate basically, no?. so we need that humidity map for 25000 feet.

so why is that altitude so weird?

question: because your trees are different than here... are the leaves upside down in those pics? when we have skies like that here, half our leaves are upside down-, like they do before a storm but we dont always get rain.
 

Trailspotter

Senior Member.
As for the turboprop, it is not unusual. I recently posted here the pics of a similar lower altitude contrail from the same type aircraft (Q400). As for the other two aircraft, I think these probably left aerodynamic contrails that persisted afterwards. It would be interesting to do a systematic study of aerodynamic contrail altitudes.
 

Trailblazer

Moderator
Staff member
Then, later that day, nearby in Cameron Park, Looking NW I saw:
Those look like aerodynamic contrails. They have that kind of "flat" look to them.

Edit to add, I have noticed the "cumulus" type of contrails before. I posted a photo in the pictures thread back in December: https://www.metabunk.org/photos-of-...t-you-took-yourself.t1487/page-12#post-137264



I didn't note the altitude of the planes responsible, though. But it was on a chilly December day, so the contrail threshold could have been quite low.
 
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Mick West

Administrator
Staff member
the only reason contrails dont persist once they form, is because they evaporate basically, no?. so we need that humidity map for 25000 feet.

so why is that altitude so weird?
Because for "regular" exhaust contrails to form, it needs to be around -40 or below, and at 25,000 feet (7,620m) over Sacramento this was not the case.

This is today's forecast over Sacramento, for a simple visual:
http://www.usairnet.com/cgi-bin/Win...AC&Submit=Get+Forecast&hour=06&course=azimuth


The closest two sounding stations to Sacramento are Oakland (60 miles SW) and Reno (110 miles NW), too far for any meaningful forecast of local humidity condition, but give a good idea of temp. Oakland is the closest. The soundings were a couple of hours before the contrails.

Oakland:
http://weather.uwyo.edu/cgi-bin/sou...AR=2015&MONTH=05&FROM=2900&TO=2912&STNM=72493
At 25,000 feet the temp was -22.6°C, and -40°C occurred at 35,000 feet

Reno:
http://weather.uwyo.edu/cgi-bin/sou...AR=2015&MONTH=05&FROM=2900&TO=2912&STNM=72493
At 25,000 feet the temp was -24.5°C, and -40°C occurred at 32,200 feet

So it's simply too warm for a traditional persistent exhaust contrail to form.

Now this is important from a "chemtrail" debunking point of view, as people hear that the criteria is -40°, and then we see multiple huge persistent contrails forming at -22.5°C (-8.5°F). So they assume they are "chemtrails", and some debunkers assume they made a mistake in identifying the plane.

So the question arises, what exactly is going on here. It looks like an aerodynamic contrail (from the full wing surface), maybe combined with exhaust humidity, in atmospheric conditions that are very near or in water supersaturation (i.e. relative humidity above 100%).

The key clue here is that the trails seem to form in (or very near) a layer of what look like rather puffy cirrocumulus clouds. I think clouds like these need water supersaturation to form, so the RH near those clouds must be approaching or above 100%.

Now I'd heard of persistent aerodynamic contrails (PAC) before, but I'd never seen one. It may be that there are parts of the world where the conditions for PAC are more favorable, and so they more commonly see lower altitude contrails - perhaps much lower in parts of Europe.
 

Mick West

Administrator
Staff member
Reading this:
http://www.atmos-chem-phys.net/13/10847/2013/acp-13-10847-2013.pdf


For formation they give a minimum temp of 230K, -43°C, -45F, which isn't a problem

Going by the Oakland soundings, the pressure at 25,000 feet (7620m) was about 400 hPa, normal. According to their chart, this gives a maximum formation temperature of around 246K, -27°C, -17°F.

The sounding data seems a little higher than this, but not significantly (especially since they are just ballparking the pressure drop)

Note these criteria are for the formation of an ice aerodynamic contrail, as an ice contrail requires a drop below the supercooling limit of pure water.
 
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deirdre

Senior Member.
This is today's forecast over Sacramento, for a simple visual:
doesnt that say -40 at 25000? or does windchill not count?

According to their chart, this gives a maximum formation temperature of around 246K, -27°C, -17°F.
so this is saying aerodynamic contrails can form at -17Farenheit or colder?

is that because theres no left over engine heat in aerodynamic contrails?

Your Cameron Park photo does look like they could be aerodynamic as they are more translucent then contrails i normally see. And the first time i pointed out a contrail to my mom (summer) and we were watching it (persistant), you wouldnt believe how big it grew. opaque white thick and BIG BIG, like 500-600x its original size in about 15 minutes. It didnt spread out/thin out. It GREW. It was pretty impressive.

But still i dont see why windchill doesnt count.
 

Mick West

Administrator
Staff member
doesnt that say -40 at 25000? or does windchill not count?
It does not. Windchill just affects how cold it feels. It's irrelevant to cloud physics (except that it indicates it is windy, which moves the clouds around)
http://en.wikipedia.org/wiki/Wind_chill
 

Mick West

Administrator
Staff member
The local El Dorado skywatch also noticed these contrails:





This one is very like my first photo:


The V was pretty dramatic, I'm sure there are many more photos of it.
 

Mick West

Administrator
Staff member
This one from EDCSW (a private group, so I can't link to it) shows the the "ribbon" quality of an aerodynamic contrail.


Then later:
 

Mick West

Administrator
Staff member
There's non-ice contrails? Aren't they all ice-crystals?
No, for example the aerodynamic contrails that form when a plane is landing are liquid water.


What's not clear is if a liquid contrail can be persistent, i.e. can a plane make liquid clouds which don't evaporate when the pressure returns to normal. I think that's possible if the air were just very slightly supersaturated, and trending upwards in saturation because of air movement.

But these here (in the OP) I think are probably ice. The V has a solar halo segment.
 
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Mick West

Administrator
Staff member
I saw another Aerodynamic contrail today, possible mixed aerodynamic/exhaust.

This plane was near overhead in the first photo:


Camera Time 14:33:10 UTC 21:26:36
(Camera is 6:34 fast)

This is about two seconds after it started:

Camera time 14:33:51 UTC 21:27:17

The last pic before it went behind the trees:

Camera time 14:34:03 UTC 21:27:29

Here's an extreme contrast enhancement to show it is aerodynamic (starts at the wing)


About six minutes after that it had spread out.


The plane was a KLM 747 from SFO.


Altitude is a different story today though, as the plane did not start to con until it was at about 33,000 feet, and yet it was still an aerodynamic contrail, not an exhaust contrail.

Also interesting, 33,000 feet is the altitude at which it leveled off, so before that point, the wings would have been producing more lift. It's not clear if this is related.
 
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Trailspotter

Senior Member.
Reading this:
http://www.atmos-chem-phys.net/13/10847/2013/acp-13-10847-2013.pdf
I've looked at the Figure 1, it lists only medium-size aircraft:
Screen shot 2015-05-30 at 12.56.29.png

I think that for heavier planes, like B747 and A340, the pressure difference is probably higher than the values used in the paper. Compared to medium size planes, like B737, their maximum and operational weights have increased by a greater factor than their wing surface area.
 

Trailblazer

Moderator
Staff member
Just bumping this thread. This afternoon I saw this plane over Berkshire, UK. According to FR24 (and Planefinder) it was Delta 123, a 767 at 26,000 feet, but it was leaving a contrail. Unfortunately I only had my phone to photograph it, and the autofocus caught the nearby trees on this shot.

image.jpeg

The trail persisted, and initially had well-defined pendules (it's the upper trail in this photo). Four minutes after first photo:

image.jpeg

And nine minutes after the first one:
image.jpeg

This had to be the plane, unless there was a higher one in almost exactly the same place that didn't show up on flight trackers. First photo was taken at 12:48 UTC, from the circled location.

upload_2015-10-25_17-11-39.png
 

Mick West

Administrator
Staff member
Just bumping this thread. This afternoon I saw this plane over Berkshire, UK. According to FR24 (and Planefinder) it was Delta 123, a 767 at 26,000 feet, but it was leaving a contrail. Unfortunately I only had my phone to photograph it, and the autofocus caught the nearby trees on this shot.
It still has the look of an aerodynamic contrail - a more even "ribbon" trail, and then even separation later.


All the aerodynamic contrails I've been seeing since I moved from Los Angeles to near Sacramento has made me rethink their relative frequency, and the focus that people put on exhaust contrails, and the required conditions for their formation. I tended to assume more that people were getting the altitude wrong a lot of the time, but there's actually a lot more contrails in the 20,000 to 30,000 foot range than your would think (at least round here). And in colder locations the formation altitude can be much lower.
 

Trailspotter

Senior Member.
All the aerodynamic contrails I've been seeing since I moved from Los Angeles to near Sacramento has made me rethink their relative frequency, and the focus that people put on exhaust contrails, and the required conditions for their formation. I tended to assume more that people were getting the altitude wrong a lot of the time, but there's actually a lot more contrails in the 20,000 to 30,000 foot range than your would think (at least round here). And in colder locations the formation altitude can be much lower.
The same is here, in East Anglia. I stayed home this Easter break and entertained myself by spotting planes and their contrails, aided by FR24 on my laptop. The storm Katie, which passed across our region early morning today, stirred the atmosphere: there were clouds at many different levels, but also clear sky patches. There also were 'invisible' clouds - parcels of clear humid air, which supported the formation and persistence of contrails. However, at altitudes above 28,000 ft, the air appeared to be rather dry - I could not detect a single persistent contrail from the planes cruising in that altitude range. In contrast, I've spotted quite a few short persistent trails left at lower altitude, generally, around 25,000 ft:IMG_0178.JPG
IMG_0175.JPG
IMG_0176.JPG
IMG_0186.JPG
IMG_0187.JPG
Unfortunately, in the most cases, I failed to spot the planes that left those contrails. They vanished in the clear sky as soon as they exited the 'invisible clouds'. It usually happened well before I managed to locate the right patch of the sky, where the approaching planes were to appear. Nevertheless, as the contrails appeared exactly where they were expected, I am fairly certain that they belong to the flights I followed on FR24:
Screen Shot 2016-03-28 at 16.48.42.png
Screen Shot 2016-03-28 at 16.53.17.png

I haven't seen before so many planes flying in the vicinity at around 25,000 ft. Planes bound to the nearby London airports in Stansted and Luton usually fly lower on approach or take-off. The planes in 25,000 ft range were mostly from more distant airports in Birmingham and Norwich, the air traffic from which apparently have increased (perhaps due to Easter holidays?)

In three cases, I managed to get the planes. All three were Q400 turboprops that do not fly above 25,000 ft. But this is a different story:
IMG_0193.JPG
 
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Trailblazer

Moderator
Staff member
I also noticed lots of cumuliform contrails in Hampshire yesterday. I was out and about with the family so couldn't really check them out but they seemed to be forming as you described, and looked low (not that judging by eye is in any way reliable!)

In some cases they looked to be forming inside existing clouds.
 
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