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Contrail morphology transition 2 cirrus uncinus

Contrail morphology transition 2 cirrus uncinus

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  • uploaded: Aug 24, 2010
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Contrails to Cirrus—Morphology, Microphysics, and Radiative Properties


This work is two pronged, discussing 1) the morphology of contrails and their transition to cirrus uncinus,
and 2) their microphysical and radiative properties. It is based upon the fortuitous occurrence of an unusual
set of essentially parallel contrails and the unanticipated availability of nearly simultaneous observations by
photography, satellite, automated ground-based lidar, and a newly available database of aircraft flight
tracks. The contrails, oriented from the northeast to southwest, are carried to the southeast with a component
of the wind so that they are spread from the northwest to southeast. Convective turrets form along
each contrail to form the cirrus uncinus with fallstreaks of ice crystals that are oriented essentially normal
to the contrail length. Each contrail is observed sequentially by the lidar and tracked backward to the time
and position of the originating aircraft track with the appropriate component of the wind. The correlation
coefficient between predicted and actual time of arrival at the lidar is 0.99, so that one may identify both
visually and satellite-observed contrails exactly. Contrails generated earlier in the westernmost flight corridor
occasionally arrive simultaneously with those formed later closer to the lidar to produce broader cirrus
fallstreaks and overlapping contrails on the satellite image. The minimum age of a contrail is 2 h and
corresponds to the longest time of travel to the lidar. The lag between the initial formation of the contrail
and its first detectability by Moderate-Resolution Imaging Spectroradiometer (MODIS) is 33 min, thus
accounting for the distance between the aircraft track and the first detectable contrail by satellite. The lidar
also provides particle fall speeds and estimated sizes, optical extinction coefficients, optical thickness ( 
0.35), and ice water path (IWP  8.1 g m2). These values correspond to the lower range of those found
for midlatitude cirrus by Heymsfield et al. The ice water per meter of length along the cloud lines is 103–104
times that released by typical jet aircraft. The synthesis of these findings with those of prior investigators
provides confidence in the present results. Various authors find that contrail-generated cirrus such as
reported here contribute to net regional warming.

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