The evolution of microphysical and optical properties of an A380 contrail in the vortex phase

The contrail from a large-body A380 aircraft has extensively been probed in the vortex and early dispersion regime with in situ instruments to measure microphysical and optical properties of contrail ice particles on the DLR research aircraft Falcon. Concentrations up to 340 cm−3 of ice particles with diameters d >0.9 μm and extinction coefficients up to 7.0 km−1 were measured inside the plume. Initially the primary vortices were sampled about 270 m below the A380 flight altitude at contrail ages of 70 to 120 s in ice subsaturated conditions, followed by measurements in the secondary wake with contrail ages of 120 to 220 s at conditions near ice saturation. In the primary vortices the mean effective diameter was 3.5 μm and the maximum ice water content (IWC) was 7.0 mg m−3 increasing with altitude and ice saturation in the secondary wake to 4.8 μm and 10.0 mg m−3. The asymmetry parameter was found to decrease systematically with contrail age (and altitude) from 0.87 to 0.80 indicating that ice crystals become more and more aspherical during ice crystal growth. In addition, an inversion approach was used to retrieve the ice particle size distribution and the partitioning between spherical and aspherical particles. In the young primary vortex 100% of the ice particles were of spherical shape, whereas partitioning coefficients of 68% and 44% were found in the more aged secondary wake. The extrapolation of our results to older contrails under similar meteorological conditions suggests that contrails with ages over 5 min may be dominated by aspherically-shaped ice particles typical for natural mid latitude cirrus.