Eyjafjallajkull ash concentrations derived from both lidar and modeling

Following the eruption of the Icelandic volcano Eyjafjallajkull on the 14 April 2010, ground-based N-2-Raman lidar (GBL) measurements were used to trace the temporal evolution of the ash plume from 16 to 20 April 2010 above the southwestern suburb of Paris. The nighttime overpass of the Cloud-Aerosol LIdar with Orthogonal Polarization onboard Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation satellite (CALIPSO/CALIOP) on 17 April 2010 was an opportunity to complement GBL observations. The plume shape retrieved from GBL has been used to assess the size range of the particles size. The lidar-derived aerosol mass concentrations (PM) have been compared with model-derived PM concentrations held in the Eulerian model Polair3D transport model, driven by a source term inferred from the SEVIRI sensor onboard Meteosat satellite. The consistency between model and ground-based wind lidar and CALIOP observations has been checked. The spatial and temporal structures of the ash plume as estimated by each instrument and by the Polair3D simulations are in agreement. The ash plume was associated with a mean aerosol optical thickness of 0.1 +/- 0.06 and 0.055 +/- 0.053 for GBL (355 nm) and CALIOP (532 nm), respectively. Such values correspond to ash mass concentrations of similar to 400 +/- 160 and similar to 720 +/- 670 mu g m(-3), respectively, within the ash plume, which was lower than 0.5 km in width. The relative uncertainty is similar to 75% and mainly due to the assessment of the specific cross-section assuming an aerosol density of 2.6 g cm(-3). The simulated ash plume is smoother leading to integrated mass of the same order of magnitude (between 50 and 250 mg m(-2)).