Contrails

Processes.jpg: This graph illustrates the processes which are responsible for the development of contrails. The hot exhaust gases of the engines are isobarically mixed with the cold surrounding air. The released sulphuric acid vapour condenses on soot particles which are also emitted. So droplets consisting of liquid sulphuric acid are formed on a soot particle core by heterogenous nucleation. However under certain conditions gaseous sulphuric acid can also directly form sulphuric acid droplets via homogenous nucleation. In addition clusters of charged molecules in the exhaust gas support droplet formation. Once the droplets are generated, they will grow by absorption of water vapour molecules (condensation). If the air is cold and humid enough, the droplets can grow to large sizes and freeze to ice particles. Only now the contrail becomes visible.

Contrails1-4.jpg: The images which were taken from the ground show different stages of a contrail. The numeration fits with the temporal sequence of around 20 minutes.

Contrails5.jpg displays a sky with long contrails. This indicates high humidity at an altitude of approximately 10 to 12 km. Here the supersaturation is high enough to prevent ice-particles which have been once formed in the contrail to evaporate for a longer period of time.

Contrails6+7.jpg present contrails which are momentarily formed behind the aircrafts. They were generated in dry air and thus quickly evaporate so that they are very short. In the images the long, broad ice-cloud stripes are "aged contrails" occurring in a humid air layer.

Contrails with different lengths often appear next to each other. This indicates a layering of air masses with significantly varying humidity in the upper troposphere. The stripy structure of the broad contrail in Contrail7.jpg is caused by sedimentation of large ice particles from the clouds top down in an air layer with shear flow.

Contrails8.-10.jpg: Different stages of a contrail, observed from the ground. In contrast to Contrails1.jpg these images show a contrail which quickly (in around 10 min) evaporates above an Altocumuls translucidus layer. The contrail occurs in a region of strong horizontal wind shearing. Therefore it has a clearly visible wave structure.

Contrails11-.14.jpg: Some more contrails in the upper troposphere which is supporting ice particle formation are shown here. For Contrails14.jpg a 200 mm objective was used with an exposure time of 1/13 s. During this period of time the aircraft moves 17 m forward. Therefore it is obvious why the reproduction is only blurred.

A large-capacity jet which has started at Frankfurt Airport in a distance of 40 km is displayed in Contrail15.jpg. The aircraft was pictured with a 200 mm objective from the ground.

Contrails16-18.jpg: This contrail was pictured from an airliner at a cruising altitude of 11 km. The aging contrail of another airplane was passed with a small vertical dislocation (most probably 100 m). The line vortex structure dissolving as a consequence of Taylor instabilities can be noticed.

Passing1-4.jpg:
Since air corridors were re-organized, it happens more often that aircrafts meet each other in passages, because the single regions for each of them are narrower scaled. Here one can see a sequence of images within a time period of seven minutes where a faster Boeing B747 passed our aircraft in a neighboured flight level. A camera objective with a focal length between 104 and 200 mm was used.

Processes.jpg: J. Curtius, Mainz, Germany, May 2002

Contrails1-5.jpg: S. Borrmann, Ingelheim, Germany, May 1999

Contrails6+7.jpg: S. Borrmann, Pulpit Rock, Carinthia, Austria, 2 January 2002

Contrails8-10.jpg: S. Borrmann, Ingelheim, Germany, March 1999

Contrails11-15.jpg: S. Borrmann, Ingelheim, Germany, 29 May 2004, 7:59 p.m.

Contrails16-18.jpg: S. Borrmann, flight from Frankfurt to Philadelphia, 6 December 2004, 2:03 p.m.

Passing1-4.jpg: S. Borrmann, flight from Frankfurt to Philadelphia, 6 December 2004, 6:49:56 p.m. to 6:56:07 p.m.