Contrails to Cirrus – Morphology, Microphysics, and Radiative Properties.

By

David Atlas [1][2]

Laboratory for Atmospheres

NASA Goddard Space Flight Center

Goddard Earth Science and Technology Center ,

University of Maryland Baltimore County ,

NASA Goddard Space Flight Center

National Institute of Aerospace .

NASA Langley Research Center

June 27, 2005

Abstract

      This work is two-pronged: 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, automatated ground based lidar, and a newly available database of aircraft flight tracks. The contrails, oriented from NE to SW, are carried to the SE with a component of the wind so that they are spread from NW to SE. Convective turrets form along each contrail to form the cirrus uncinus with fallstreaks of ice crystals which are oriented essentially normal to the contrail length. Each contrail is observed sequentially by the lidar and tracked backwards 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 hrs 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 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 (<t>=0.35), and ice water path (<IWP>=8.1 g m^-2). These values correspond to the lower range of those found for mid-latitude cirrus by Heymsfield et al (2003). The ice water per meter of length along the cloud lines is 10³ to 10⁴ greater than 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.