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Optical properties of contrail-induced cirrus. Discussion of unusual halo phenomena

: Sussmann, R.


Applied optics 36 (1997), No.18, pp.4195-4201 : Ill., Lit.
ISSN: 0003-6935
ISSN: 1539-4522
ISSN: 1559-128X
Journal Article
Fraunhofer IFU; 2002 in Helmholtz-Gesellschaft integriert
aircraft; climatic impact; contrail; crystal growth; halo phenomena; ice crystals; optical properties; relative humidity; remote sensing; scattering phase function

Photographs of a 120 degree parhelion and a 22 degree parhelion within persistent contrails are presented. These phenomena result from hexagonal plate-shaped ice crystals oriented horizontally with diameters between 300 mu m and 2 mm. From our observations and reinvestigation of previous reports, we conclude that a subset of the population in persistent contrails can consist of highly regular, oriented, hexagonal plates or columns comparable to the most regular crystals in natural cirrus clouds. This is explained by measured ambient humidities below the formation conditions of natural cirrus. The resulting strong azimuthal variability of the scattering phase function impacts the radiative transfer through persistent contrails.