Characterization of the Eyjafjallajِkull ash-plume: Potential of lidar remote sensing

Observations of the dispersion of volcanic ash clouds and their optical and microphysical characterization are essential for climate research and air traffic. This became obvious during the Eyjafjallajökull-eruption in April 2010. In this paper we report on continuous measurements with two EARLINET Raman- and depolarization lidars conducted at Maisach close to Munich, Germany. By means of range corrected signals the temporal development of the ash-plume could be documented in near real-time. They confirmed results from a chemistry transport model (MCCM). The optical characterization includes the backscatter coefficient at three wavelengths, and the extinction coefficient and particle linear depolarization ratio at two. The maximum extinction coefficient of the ash layer over Maisach was 0.75 km−1 and wavelength independent, the particle linear depolarization ratio was about 37%. This is a strong indication of large non-spherical particles. An inversion of the optical data derived from the lidar measurements led to a maximum mass concentration of approximately 1.1 mg m−3 over Maisach. As a consequence of the ambiguity of the inversion process and measurement-errors, relative uncertainties are between 30% and 50%.