• aerosols;
  • lidar;
  • satellite;
  • volcano

[1] The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) is an elastic backscatter lidar carried on the CALIPSO satellite. CALIOP observations between 15 and 20 April 2010 of volcanic ash plumes following the eruption of the Icelandic Eyjafjallajökull volcano are reported here. While CALIOP has limited spatial coverage due to nadir-only sampling, ash plumes were observed by CALIOP over a wide region - from the North Atlantic Ocean to eastern Europe - during both day and night. Due to its nadir-only view, however, CALIOP did not sample the densest ash plumes which were observed by passive satellite sensors and ground-based lidar. Lidar depolarization and spectral backscatter signatures are used to discriminate ash layers from clouds. Most ash was observed in thin layers of laminar appearance with thicknesses ranging from 0.4 km to a little more than 1 km and at relatively low altitudes, between 1 and 7 km. Most layers reported here produced strong lidar depolarization, indicating a predominance of ash over sulfate aerosol in the plumes. Estimates of lidar extinction-to-backscatter ratio allow the retrieval of profiles of ash optical properties. Layers were observed with mean optical extinction ranging from 0.03 km−1 to nearly 1 km−1. Combined with an estimate of mass extinction efficiency, mass concentration profiles can also be estimated. These observations of the three-dimensional dispersion of the plume are complementary to observations from passive satellite instruments and ground-based lidars, and can be useful for verification of dispersion models such as those used by the Volcanic Ash Advisory Centers.