Contrail microphysics

Contrails are products of aircraft emissions in the upper troposphere at temperatures of about -40°C or below, which are among the most visible human influences on the Earth's climate. Initially, the microphysical properties of contrails differ from those of natural cirrus, but with age contrails may lose their shape and spread, becoming virtually indistinguishable from natural cirrus, both visually and perhaps also in their microphysical properties. Contrail microphysical properties include ice water content (IWC), the total ice particle number concentration (N_t) ice particle size distributions (PSD), ice particle effective radii and ice particle shapes. Observations of the ice crystal shapes during the early phase of contrail formation and beyond are sparse. Studies have revealed that measurements of small ice crystals can be artificially enhanced as a result of several hundred micron or larger particles either shattering on the inlets or arms of optical spectrometers or bouncing or shattering on upstream surfaces of the measurement aircraft.