Dual-wavelength linear depolarization ratio of volcanic aerosols: Lidar measurements of the Eyjafjallajökull plume over Maisach, Germany

Abstract

The ash plume of the Eyjafjallajökull eruption in April 2010 offered an exceptional opportunity to assess the potential of advanced lidar systems to characterize the volcanic aerosols. Consequently, the plume was continuously observed in the framework of EARLINET. In this paper we focus on the EARLINET-Raman-depolarization-lidar measurements at Maisach near Munich, Germany. From these data sets the lidar ratio S p and the particle linear depolarization ratio δ p at two wavelengths (355nm and 532nm) were retrieved. These quantities can be used to characterize volcanic aerosols and to establish criteria for the discrimination from other aerosol types. In the pure volcanic ash plume, observed until noon of 17April, wavelength independent values of δ p as high as 0.35 <0.38, indicating non-spherical particles, were found, and lidar ratios of 50 <60 sr at 355nm and 45 <55 sr at 532nm. Later, volcanic aerosols were mixed into the boundary layer. This mixture showed in general lower values of δ p as expected from the contribution of boundary layer aerosols. Especially noteworthy is the increase of δ p with wavelength, when volcanic ash was mixed with small spherical particles. © 2011 Elsevier Ltd.