In situ observations of contrail microphysics and implications for their radiative impact

In this study we present the microphysical characteristics of 21 jet contra il clouds sampled in situ and examine the possible effects of exhaust on na tural cirrus and radiative effects of contrails. Microphysical samples were obtained with Particle Measuring Systems (PMS) 2D-C, 1D-C, and FSSP probes . About one half of the study contrails were generated by the sampling airc raft, a Cessna Citation, primarily at times of 3-15 min after generation; t he source and age of the others is unknown. On average, the contrails conta ined particles of mean diameter of the order of 10 mu m in concentrations e xceeding 10,000 L-1. Contrails embedded in natural cirrus appeared to have little effect on the natural cloud microphysics. Anomalous diffraction theo ry was used to model radiative properties of sampled contrails. The contrai l cirrus showed considerably more spectral variation in extinction and abso rption efficiencies than natural cirrus because of the large numbers of sma ll crystals in contrails. Embedded contrails also displayed greater emissiv ity and emission than natural cirrus and a greater spectral variation in tr ansmission.