Contrails in the Stratosphere

[Jazzy]

You can see how it starts becoming significant near the bank of cloud.

And I'm amazed at what can only be a mass of RAIN beneath it. Maybe there's a volumetric shadow in there too...

 

[Jazzy]

Hmm, maybe we should revisit this in the morning

Just you.

And the authors. LOL.

 

[Jay Reynolds]

I happened across a very fine slide set about the jet streams:
http://www.pbs.org/wgbh/nova/vanished/media/jetstream.swf

 

[Billzilla]

Do you remember what latitude you were cruising . . . when you were in the 30 to 40,000 feet situation . . .

Also, wouldn't the stratosphere be around 58,000 feet above most of India . . . if the contrail is in the stratosphere . . . how high was it??

I think it was around 20° north or so, not sure as it was a long time ago.
I doubt very much the bottom of the stratosphere would have been that high but I can't confirm for sure sorry. It's more commonly in the high 30's to low 40's or so. That airliner in front of us would have easily been in the 40's though.

 

[Jay Reynolds]

Perhaps the largest set of empirical measurements of upper tropospheric(UT) and lower stratospheric(LS) water vapor were taken during the MOZAIC campaign in 1999.

Over 5000 flights of instrumented commercial airliners cruising in the 175-275 HPa levels produced the dataset.

They identified stratospheric altitude by abundance of ozone

They found that ice supersaturation in the UT averaged 15%, but in the LS only 2%.

http://hal.archives-ouvertes.fr/docs/00/32/91/39/PDF/angeo-17-1218-1999.pdf

It seems clear to me that the data is showing that conditions favorable to persistent contrails are more prevalent in the UT and much less in the LS.

 

[George B]

Perhaps the largest set of empirical measurements of upper tropospheric(UT) and lower stratospheric(LS) water vapor were taken during the MOZAIC campaign in 1999.

Over 5000 flights of instrumented commercial airliners cruising in the 175-275 HPa levels produced the dataset.

They identified stratospheric altitude by abundance of ozone

They found that ice supersaturation in the UT averaged 15%, but in the LS only 2%.

http://hal.archives-ouvertes.fr/docs/00/32/91/39/PDF/angeo-17-1218-1999.pdf

It seems clear to me that the data is showing that conditions favorable to persistent contrails are more prevalent in the UT and much less in the LS.

Seems persistent contrails in the lower stratosphere are not impossible but probably not common either . . . and that is consistent with what Dr Minnis indicated . . .

 

[Jazzy]

Perhaps the largest set of empirical measurements of upper tropospheric(UT) and lower stratospheric(LS) water vapor were taken during the MOZAIC campaign in 1999.
Over 5000 flights of instrumented commercial airliners cruising in the 175-275 HPa levels produced the dataset. They identified stratospheric altitude by abundance of ozone. They found that ice supersaturation in the UT averaged 15%, but in the LS only 2%.
It seems clear to me that the data is showing that conditions favorable to persistent contrails are more prevalent in the UT and much less in the LS.

I'm not disagreeing with you, Jay.

I am pointing out that paper was no help to anyone.

That final graph, and the conclusion drawn from it, are in direct contradiction with each other. One or the other must be wrong. We have no way of knowing which.

My gut tells me the conclusion is wrong, and the diagram correct. That's the "gut" that holds on to what laminar flow really is, namely a property of the stratosphere.

Nope. I've changed my mind. The conclusion they drew is correct. The Y axis they drew is pants. They didn't multiply by a negative factor in the crunch, and didn't bother to amend the mistake.

 

[Jay Reynolds]

Based on the data we have seen, it looks to me like these generalizations exist:
-the stratosphere is generally dryer than the troposphere
-ice supersaturation is more common in the troposphere(~15%) than the stratosphere(~2%)
-high altitude jet traffic takes place in both regions
-the likelihood of persistent contrails is probably greater in the troposphere

- the jet streams generally run close to the tropopause, but excursions might take it above or below that level

Can we agree on these generalizations?

 

[Jazzy]

Based on the data we have seen, it looks to me like these generalizations exist:
- the stratosphere is generally dryer than the troposphere
- ice supersaturation is more common in the troposphere(~15%) than the stratosphere(~2%)
- high altitude jet traffic takes place in both regions
- the likelihood of persistent contrails is probably greater in the troposphere
- the jet streams generally run close to the tropopause, but excursions might take it above or below that level
Can we agree on these generalizations?

We certainly can. (I shall rant offstage.)

 

[Mick West]

Based on the data we have seen, it looks to me like these generalizations exist:
-the stratosphere is generally dryer than the troposphere
-ice supersaturation is more common in the troposphere(~15%) than the stratosphere(~2%)
-high altitude jet traffic takes place in both regions
-the likelihood of persistent contrails is probably greater in the troposphere

- the jet streams generally run close to the tropopause, but excursions might take it above or below that level

Can we agree on these generalizations?

I'd quibble a bit with the meaning of the 15% and 2%. Firstly the number in your source is 13.5%, and the 15% is referring to the mean supersaturation level not frequency (i.e. 115% RHi).

Mean supersaturation in supersaturated regions amounts to about 15%, whereas ice nucleation would need on the average a supersaturation of about 30%. This explains the frequent observation of persistent contrails in otherwise clear air.

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Secondly it's a percentage of the data, and it's not clear how that translates to an amount of supersaturation (i.e. is it just how many times they found it, and/or is that proportional to the actual volume of supersaturated air?).

13.5% of the analysed data imply ice supersaturation, in the stratosphere (presumably just above the tropopause) 2% of the data imply ice supersaturation. This value depends on the definition of the tropopause.

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Also the data in that study comes from MOZAIC instruments, so by definition it's only sampling where aircraft fly. Of course that's great for contrail prediction, but we can't necessarily extrapolate the data beyond those altitudes. And it might introduce biases

The MOZAIC instruments are installed on commercial airliners, not on research aircraft. The main task of commercial airlines is of course to transport people and freight, not to perform measurements in the atmosphere. The data sample that is evaluated here may therefore be biased in several respects due to habits of international aviation. For instance, pilots of North-Atlantic flights try to utilise or avoid the jet stream in order to save fuel and time. Properties of the jet stream zone are therefore expected to have a relatively large weight in the data sample.

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Certainly though it implies that the majority of contrails will form in the troposphere.