Abstract
Abstract. A contrail from a large-body A380 aircraft at cruise in the humid upper troposphere has been probed with in-situ instruments onboard the DLR research aircraft Falcon. The contrail was sampled during 700 s measurement time at contrail ages of about 1–4 min. The contrail was in the vortex regime during which the primary wake vortices were sinking 270 m below the A380 flight level while the secondary wake remained above. Contrail properties were sampled separately in the primary wake at 90 and 115 s contrail age and nearly continously in the secondary wake at contrail ages from 70 s to 220 s. The scattering phase functions of the contrail particles were measured with a polar nephelometer. The asymmetry parameter derived from these data is used to distinguish between quasi-spherical and aspherical ice particles. In the primary wake, quasi-spherical ice particles were found with concentrations up to 160 cm−3, mean effective diameter Deff of 3.7 μm, maximum extinction of 7.0 km−1, and ice water content (IWC) of 3 mg m−3 at slightly ice-subsaturated conditions. The secondary and primary wakes were separated by an almost particle-free wake vortex gap. The secondary wake contained clearly aspherical contrail ice particles with mean Deff of 4.8 μm, mean (maximum) concentration, extinction, and IWC of 80 (350) cm−3, 1.6 (5.0) km−1, and 2.5 (10) mg m−3, respectively, at conditions apparently above ice-saturation. The asymmetry parameter in the secondary wake decreased with contrail age from 0.87 to 0.80 on average indicating a preferential aspherical ice crystal growth. A retrieval of ice particle habit and size with an inversion code shows that the number fraction of aspherical ice crystals increased from 2% initially to 56% at 4 min contrail age. The observed crystal size and habit differences in the primary and secondary wakes of an up to 4 min old contrail are of interest for understanding ice crystal growth in contrails and their climate impact. Aspherical contrail ice particles cause less radiative forcing than spherical ones.
Highlights
Contrails may have a climate impact similar in magnitude to the radiative forcing from aircraft CO2 emissions (Lee et al, 2009, 2010; Burkhardt and Karcher, 2011; Schumann et al, 2012)
Four particle instruments were used in under-wing stations to detect microphysical and optical properties of contrails and cirrus clouds: (1) the Polar Nephelometer (PN), (2) the Cloud Particle Imager (CPI), (3) the 2D-C, all operated by LaMP, and (4) the FSSP-300 operated by DLR
The method to calibrate the FSSP size for spherical and aspherical particles is presented in Appendix A together with definitions of the microphysical parameters used in this study
Summary
Contrails may have a climate impact similar in magnitude to the radiative forcing from aircraft CO2 emissions (Lee et al, 2009, 2010; Burkhardt and Karcher, 2011; Schumann et al, 2012). Febvre et al (2009) measured ice particles in young contrails using a polar nephelometer and size spectrometers similar to the present study and found that the optical properties were controlled mainly by quasi-spherical ice particles with Deff below 5 μm, while larger aspherical ice crystals govern the optical properties of 20 min old contrails. Size, shape and extinction of contrails in the vortex phase is crucial for the initialization and validation of contrail models, since it determines contrail evolution (Lewellen and Lewellen, 2001; Unterstrasser et al, 2008; Unterstrasser and Gierens, 2010; Paugam et al, 2010; Naiman et al, 2011; Schumann, 2012). A closure study between different in-situ instruments is given in Appendix A
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