During the April 1996 SUCCESS field campaign, our ground-based polarization lidar studied a variety of contrails ranging from a new NASA DC-8 contrail to persisting contrails from commercial jet aircraft that had spread into an almost invisible cirrostratus sheet. What distinguishes these contrails from natural cirrus is their tendency to remain thin (~50--500 m), and to generate strong laser backscattering and depolarization, often along with solar coronas, even an hour or more after formation. Lidar depolarization ratios in persisting contrails ranged from ~0.3--0.7. Contrail-cirrus clouds composed of high numbers of small (20--30 &mgr;m) particles would satisfy these findings, which has implications for comprehending their radiative and climatic effects. ¿ 1998 American Geophysical Union