Contrails from Turboprop Planes at lower than typical altitudes

Trailspotter

Senior Member.
While following the evolution of an usually shaped trail (the bottom one, just above the roof), I have taken a picture of an ordinary linear contrail (the top one), which appear to be truly remarkable - it has been formed at 23,000 feet.
IMG_0882.JPG
It was left by this plane:
IMG_0881.JPG
Here is an FR24 screenshot with the identification of the plane and its altitude:
Screen shot 2015-04-20 at 19.51.37.png

I think the formation of this trail at lower than typical contrail altitudes was possible because this is a turboprop plane, which engines produce a much cooler exhaust than the jet's turbofan engines:
 
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Mick West

Administrator
Staff member
It was totally unexpected to me, but it is the fact - the altitude was only 23,000 ft:
23,000 feet is 7010m, looking at the 12Z (1PM Local Time) from Cambourne (the closest to you, but still quite a ways off),

-----------------------------------------------------------------------------
PRES HGHT TEMP DWPT RELH MIXR DRCT SKNT THTA THTE THTV
hPa m C C % g/kg deg knot K K K
-----------------------------------------------------------------------------
458.0 6330 -27.7 -46.4 15 0.13 115 18 306.8 307.3 306.8
453.0 6409 -28.5 -44.5 20 0.16 114 18 306.8 307.4 306.8
449.0 6473 -29.1 -36.1 51 0.39 113 18 306.8 308.2 306.9
423.0 6898 -32.7 -35.7 74 0.43 106 18 307.5 309.0 307.5
421.0 6931 -33.1 -36.9 69 0.39 105 18 307.4 308.8 307.4
419.0 6965 -33.5 -38.0 64 0.35 105 17 307.3 308.5 307.3
415.0 7032 -34.3 -36.2 83 0.42 106 16 307.1 308.6 307.2
412.0 7083 -34.7 -38.3 70 0.34 107 15 307.2 308.4 307.3
407.0 7169 -34.9 -50.9 18 0.09 108 14 308.0 308.4 308.0
400.0 7290 -35.9 -44.9 39 0.18 110 12 308.2 308.9 308.3
393.0 7412 -37.1 -43.1 54 0.22 123 9 308.2 309.1 308.3
392.0 7429 -37.2 -44.2 48 0.19 125 8 308.3 309.0 308.3
381.0 7625 -38.9 -56.9 13 0.05 108 19 308.6 308.8 308.6
379.0 7661 -39.2 -57.1 13 0.04 105 21 308.7 308.9 308.7
358.0 8047 -42.2 -59.5 13 0.04 125 21 309.7 309.8 309.7
351.0 8180 -43.3 -60.3 14 0.03 126 21 310.0 310.1 310.0
328.0 8633 -45.5 -61.5 15 0.03 130 20 313.0 313.2 313.0
326.0 8673 -45.8 -61.2 16 0.03 130 20 313.2 313.3 313.2
315.0 8901 -47.5 -59.5 24 0.04 123 20 313.9 314.1 313.9
311.0 8984 -48.2 -60.2 24 0.04 120 20 314.0 314.2 314.0
300.0 9220 -50.3 -62.3 23 0.03 130 19 314.3 314.5 314.4



There's a region of quite humid cold air (-34C, 83%RH). Seems quite suitable for formation of non-persistent contrail.

Cambourne RH readings seem pretty accurate, unlike most in the US.
 

Mick West

Administrator
Staff member
Running that day though my RHi calculator script shows ice supersaturated regions at that level

At 6330.0m, rh = 15.0 rhi = 19.7, temp =-27.7 dwpt = -46.4
At 6409.0m, rh = 20.0 rhi = 26.5, temp =-28.5 dwpt = -44.5
At 6473.0m, rh = 51.0 rhi = 67.9, temp =-29.1 dwpt = -36.1
At 6898.0m, rh = 74.0 rhi = 102.1, temp =-32.7 dwpt = -35.7
At 6931.0m, rh = 69.0 rhi = 95.6, temp =-33.1 dwpt = -36.9
At 6965.0m, rh = 64.0 rhi = 89.0, temp =-33.5 dwpt = -38.0
At 7032.0m, rh = 83.0 rhi = 116.3, temp =-34.3 dwpt = -36.2
At 7083.0m, rh = 70.0 rhi = 98.5, temp =-34.7 dwpt = -38.3
At 7169.0m, rh = 18.0 rhi = 25.4, temp =-34.9 dwpt = -50.9
At 7290.0m, rh = 39.0 rhi = 55.5, temp =-35.9 dwpt = -44.9
At 7412.0m, rh = 54.0 rhi = 77.8, temp =-37.1 dwpt = -43.1
At 7429.0m, rh = 48.0 rhi = 69.2, temp =-37.2 dwpt = -44.2
At 7625.0m, rh = 13.0 rhi = 19.1, temp =-38.9 dwpt = -56.9
At 7661.0m, rh = 13.0 rhi = 19.1, temp =-39.2 dwpt = -57.1
At 8047.0m, rh = 13.0 rhi = 19.7, temp =-42.2 dwpt = -59.5
At 8180.0m, rh = 14.0 rhi = 21.4, temp =-43.3 dwpt = -60.3
At 8633.0m, rh = 15.0 rhi = 23.4, temp =-45.5 dwpt = -61.5
At 8673.0m, rh = 16.0 rhi = 25.1, temp =-45.8 dwpt = -61.2
At 8901.0m, rh = 24.0 rhi = 38.2, temp =-47.5 dwpt = -59.5
At 8984.0m, rh = 24.0 rhi = 38.4, temp =-48.2 dwpt = -60.2
At 9220.0m, rh = 23.0 rhi = 37.6, temp =-50.3 dwpt = -62.3
 

Trailspotter

Senior Member.
Running that day though my RHi calculator script shows ice supersaturated regions at that level

At 6330.0m, rh = 15.0 rhi = 19.7, temp =-27.7 dwpt = -46.4
At 6409.0m, rh = 20.0 rhi = 26.5, temp =-28.5 dwpt = -44.5
At 6473.0m, rh = 51.0 rhi = 67.9, temp =-29.1 dwpt = -36.1
At 6898.0m, rh = 74.0 rhi = 102.1, temp =-32.7 dwpt = -35.7
At 6931.0m, rh = 69.0 rhi = 95.6, temp =-33.1 dwpt = -36.9
At 6965.0m, rh = 64.0 rhi = 89.0, temp =-33.5 dwpt = -38.0
At 7032.0m, rh = 83.0 rhi = 116.3, temp =-34.3 dwpt = -36.2
At 7083.0m, rh = 70.0 rhi = 98.5, temp =-34.7 dwpt = -38.3
At 7169.0m, rh = 18.0 rhi = 25.4, temp =-34.9 dwpt = -50.9
At 7290.0m, rh = 39.0 rhi = 55.5, temp =-35.9 dwpt = -44.9
At 7412.0m, rh = 54.0 rhi = 77.8, temp =-37.1 dwpt = -43.1
At 7429.0m, rh = 48.0 rhi = 69.2, temp =-37.2 dwpt = -44.2
At 7625.0m, rh = 13.0 rhi = 19.1, temp =-38.9 dwpt = -56.9
At 7661.0m, rh = 13.0 rhi = 19.1, temp =-39.2 dwpt = -57.1
At 8047.0m, rh = 13.0 rhi = 19.7, temp =-42.2 dwpt = -59.5
At 8180.0m, rh = 14.0 rhi = 21.4, temp =-43.3 dwpt = -60.3
At 8633.0m, rh = 15.0 rhi = 23.4, temp =-45.5 dwpt = -61.5
At 8673.0m, rh = 16.0 rhi = 25.1, temp =-45.8 dwpt = -61.2
At 8901.0m, rh = 24.0 rhi = 38.2, temp =-47.5 dwpt = -59.5
At 8984.0m, rh = 24.0 rhi = 38.4, temp =-48.2 dwpt = -60.2
At 9220.0m, rh = 23.0 rhi = 37.6, temp =-50.3 dwpt = -62.3

The Bombardier Q400 trail wasn't long, it has just stopped when I've taken the plane's photo. Before that the gap between engines and trail was much shorter than in the photo. However, the trail persisted for at least 20 minutes, and, unlike the "figure 5" trail, the wind carried it toward me. It seems that there were very peculiar atmospheric conditions in our region today. The Earth server forecast at 1800Z shows a 45° difference between the wind directions at 500 hPa and 250h Pa in my location.

I think that the fact that this plane is a turboprop may contribute to lowering the altitude for its contrail formation. I regularly see the planes of this type flying around. I may have seen them making contrails as well and will be checking their altitudes on FR24 from now on.

Q400
Stretched and improved 70–78 passenger version that entered service in 2000. Its 360 knot (667 km/h) cruise speed is 60–90 knots (111–166 km/h) higher than its competitors/predecessors. Powered by PW150A engines rated at 5,071 shp (3,781 kW) at maximum power (4,850 shp or 3,620 kW maximum continuous rated). The maximum operating altitude is 25,000 ft (7,600 m) for the standard version, although a version with drop-down oxygen masks is offered, which increases maximum operating altitude to 27,000 ft (8,200 m). All Q400s include the ANVS system.
Content from External Source
http://en.wikipedia.org/wiki/Bombardier_Dash_8
 
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Mick West

Administrator
Staff member
Thread split!

I'm wondering if it's largely (if not entirely) because turboprops cruise for hours at lower altitudes. So your 737s and bigger planes will only be at that altitude for a few minutes.

Hence you notice them leaving contrails at lower altitude as 99% of contrails at that altitude are turboprops, and 99.9% of higher altitude contrails are jets.

Cooler exhaust would make a difference though.
 

Trailblazer

Moderator
Staff member
23,000 feet is 7010m, looking at the 12Z (1PM Local Time) from Cambourne (the closest to you, but still quite a ways off)

Just a minor pedantic point: those soundings are for Camborne (in Cornwall), not Cambourne (in Cambridgeshire).

Nottingham is the closest sounding location to Trailspotter's location, but it only has data for 00Z (and the humidity data look very suspect, too!)
 

cloudspotter

Senior Member.
Just a minor pedantic point: those soundings are for Camborne (in Cornwall), not Cambourne (in Cambridgeshire).

Nottingham is the closest sounding location to Trailspotter's location, but it only has data for 00Z (and the humidity data look very suspect, too!)

There's this from Norwich

skewt_Norwich_006.png
 

Trailspotter

Senior Member.
I'm wondering if it's largely (if not entirely) because turboprops cruise for hours at lower altitudes. So your 737s and bigger planes will only be at that altitude for a few minutes.

Hence you notice them leaving contrails at lower altitude as 99% of contrails at that altitude are turboprops, and 99.9% of higher altitude contrails are jets.

Cooler exhaust would make a difference though.

I have searched for more examples of contrails from similar aircraft. So far my findings are limited to Q400 despite some of these turboprop planes have higher ceilings. It may well be that presumably cooler exhaust of its more efficient PW150A engines makes a difference.
 

Trailspotter

Senior Member.
Around the noon today in a sunny gap between the waves of rain I spotted an on-off contrail. As it looked like a possible aerodynamic contrail, I grabbed my camera and took a few snapshots.
IMG_0133.JPG

A close up on the plane revealed it being a turboprop, and the plane finder FR24 playback identified it yet again as a Q400 flying at a lower than typical altitude of 24,000 ft:
IMG_0136.JPG
Screen Shot 2016-03-27 at 15.00.41.png

One contrail segment formed within a high-altitude cloud persisted and moved with the cloud:
IMG_0139.JPG
IMG_0142.JPG

EDIT Replaced the Planefinder playback screenshot, in which the origin and destination of G-KKEV were apparently incorrect, with a screenshot from the FR24 playback.
 
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Trailspotter

Senior Member.
For the record, here are two of the three turboprop contrails I observed yesterday, March 28, 2016. All three were made by Q400s, with the two of them flying in the same direction at 23,000 ft one after the other:
IMG_0195.JPG
Screen Shot 2016-03-29 at 09.21.33.png

Zooming on the second plane:

Photos of the trails taken 6 and 10 minutes after the first photo above:
IMG_0199.JPG
IMG_0205.JPG
 
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