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3T3L1
Joined: 08 Mar 2001
Posts: 1344
Location: Lubbock, Texas |
 Tue Jul 24, 2001 8:55 pm
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Here are some pictures of 1987-vintage persistent contrails from the same URL:
Persistent contrails over the Atlantic Ocean west of Ireland at 0457 and 0901 UTC on 29 August 1987 and (right) the surface weather map for the area at 1200 UTC that day. The contrails were produced by aircraft on a number of adjacent routes.
----------04:57 UTC--------------------09:01 UTC----------------------12:00 UTC
  
[Edited 6 times, lastly by 3T3L1 on 07-24-2001] |
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3T3L1
Joined: 08 Mar 2001
Posts: 1344
Location: Lubbock, Texas |
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Wed Aug 22, 2001 10:35 pm
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For those who wonder why contrails form in places where there are no clouds, here's an abstract dealing with that, courtesy of LTC8K6. There is no definition of how long a "persistent" contrail lasts.
http://www.aero.obs-mip.fr/mozaic/abs12.html
quote:
A distribution law for relative humidity in the upper troposphere and lower stratosphere derived from three years of MOZAIC measurements
K. Gierens, U. Schumann, M. Helten, H. Smit and A. Marenco
Abstract. Data of three years of MOZAIC measurements made it possible to determine a distribution law for the relative humidity in the upper troposphere and lower stratosphere. 13.5% of the data were obtained in regions with ice supersaturation. Troposphere and stratosphere are distinguished by an ozone concentration of 130 ppbv as threshold. The degree of ice supersatutaion in the troposphere and the relative humidity in the stratosphere (both with respect to water and ice) are distributed exponentially. A stochastic model that naturally leads to the exponential distribution is provided. Mean supersaturation in the troposphere is about 15%, whereas ice nucleation requires 30% supersaturation on the average. This explains the frequency of ice supersaturated regions which are only marked by persistent contrails, but are otherwise free of clouds. Ice supersaturated regions are 3-4 K colder and contain more than 50% more vapour than other regions in the upper troposphere. The stratosphere is dry, as expected, having mean relative humidity over water of 12% and over ice of 23%, respectively. However, 2% of the stratospheric data indicate ice supersaturation. As the MOZAIC measurements have been obtained on commercial flights mainly between Europe and North America, the data do not provide a complete picture. But the exponential character of the distribution laws found is probably valid globally. Since water vapour is the most important greenhouse gas and since it might enhance the anthropogenic greenhouse effects via positive feedback mechanisms, it is important to represent its distribution correctly in climate models. The discovery of the distribution law of the relative humidity makes possible simple test whether the hydrological cycle in climate models is represented in an adequate way or not.
(Sources : Annales Geophysicae; Copyright 1999 by EGS Springer-Verlag)
[Edited 1 times, lastly by 3T3L1 on 08-22-2001] |
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3T3L1
Joined: 08 Mar 2001
Posts: 1344
Location: Lubbock, Texas |
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Fri Sep 07, 2001 4:22 pm
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Here are some rules for forecasting contrails. These are from "An Introduction to Forecasting Contrails," Naval Postgraduate School; MR3421; Cloud Physics; Prof. P. Durkee and Frank M. Schenk, LT USN.
http://www.met.nps.navy.mil/~durkee/MR3421/ProjectFS.pdf
When you know the temperature but not the relative humidity--
1. If temperature is less than -50°C: Forecast contrails.
2. If temperature is between -49°C and -40°C and there is upward motion: Forecast contrails.
3. If temperature is between -49°C and -40°C and there is downward motion: Forecast no contrails.
4. If temperature is above -39°C: Forecast no contrails.
If you have access to a weather map, the trough-ridge patterns aloft at ~30,000 feet predict contrail formation in these locations--
1. Low pressure areas in the upper troposphere and high pressure areas in the lower stratosphere.
2. In winter at ~30,000 feet--north of 35°N [Memphis, TN].
In summer at ~30,000 feet--north of 60°N [Seward, AK].
3. In winter at ~40,000 feet--the entire level.
4. In winter at ~55,000 feet--south of 40°N [Philadelphia, PA] and north of 60°N [Seward, AK].
In summer at ~55,000 feet--south of 45°N [Minneapolis, MN].
5. Looking downstream, on the right side of jet streams, up to about 400 miles from the axis.
6. At the tropopause level, plus or minus about 2000 feet.
7. In areas of positive vorticity advection at ~30,000 feet or where cirrus clouds are present.
[Edited 3 times, lastly by 3T3L1 on 09-07-2001] |
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3T3L1
Joined: 08 Mar 2001
Posts: 1344
Location: Lubbock, Texas |
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Fri Sep 07, 2001 4:58 pm
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From page 8 of the same paper, this is really interesting: ...contrails can occur with zero humidity if the temperature is cold enough.
Presumably these aren't persistent contrails. |
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