Microphysical Properties of Contrails and Climate Impact – Overview of the CONCERT (Contrail and Cirrus Experiment) Aircraft Missions in 2008 and 2011

One factor limiting the understanding of the climate impact from contrails is the accurate determination of their microphysical and optical properties. To this end contrails and contrail cirrus were investigated with the research aircraft Falcon during the CONCERT - Contrail and Cirrus Experiment - campaigns in November 2008 and September 2011. The contrails were produced by a different aircraft, amongst them the largest operating passenger aircraft Airbus A380, a Boeing B777 and several B737s, A340s and smaller aircraft.

The contrails were observed at altitudes between 8 and 11 km and temperatures between 213 and 229 K. They have a mean ice water content of 2 mg m-3, effective radii of 2.8 µm, and particle number densities near 200 cm-3. Independent of ambient ice super- or sub-saturation, the relative humidity in contrails rapidly relaxes to ice saturation. The evolution of the contrail ice particle shape is investigated in ageing contrails. Within the first 5 minutes of contrail lifetime, the fraction of aspherical particles increases significantly. Probability distribution functions of the contrail extinction and optical depth are used to estimate the contrail radiative forcing.

In addition the aircraft type has an impact on contrail properties, in particular on particle number densities and vertical contrail extensions, leading to higher contrail optical depth for increasing aircraft weight, as confirmed by observations and model results. We derive an analytical relationship between contrail properties, aircraft type and meteorological parameters. Near ice saturation, contrail width × optical depth scales linearly with the fuel flow rate. For higher relative humidity, we suggest a non-linear increase which is dependent on relative humidity. Our results could help to more accurately assess the climate impact from aviation using an aircraft-dependent contrail parameterization.