Detection and characterization of volcanic ash plumes over Lille during the Eyjafjallajökull eruption

Abstract

Routine sun-photometer and micro-lidar measurements were performed in Lille, northern France, in April and May 2010 during the Eyjafjallajökull volcanic eruption. The impact of such an eruption emphasized significance of hazards for human activities and importance of observations of the volcanic aerosol particles. This paper presents the main results of a joint micro-lidar/sun-photometer analysis performed in Lille, where volcanic ash plumes were observed during at least 22 days, whenever weather conditions permitted. Aerosol properties retrieved from automatic sun-photometer measurements (AERONET) were strongly changed during the volcanic aerosol plumes transport over Lille. In most cases, the aerosol optical depth (AOD) increased, whereas Ångström exponent decreased, thus indicating coarse-mode dominance in the volume size distribution. Moreover, the non-spherical fraction retrieved by AERONET significantly increased. The real part of the complex refractive index was up to 1.55 at 440 nm during the eruption, compared to background data of about 1.46 before the eruption. Collocated lidar data revealed that several aerosol layers were present between 2 and 5 km, all originating from the Iceland region as confirmed by backward trajectories. The volcanic ash AOD was derived from lidar extinction profiles and sun-photometer AOD, and its maximum was estimated around 0.37 at 532 nm on 18 April 2010. This value was observed at an altitude of 1700 m and corresponds to an ash mass concentration (AMC) slightly higher than 1000 μg m⁻³ (±50%). An effective lidar ratio of ash particles of 48 sr was retrieved at 532 nm for 17 April during the early stages of the eruption, a value which agrees with several other studies carried out on this topic. Even though the accuracy of the retrievals is not as high as that obtained from reference multiwavelength lidar systems, this study demonstrates the opportunity of micro-lidar and sun-photometer joint data processing for deriving volcanic AMC. It also outlines the fact that a network of combined micro-lidars and sun photometers can be a powerful tool for routine monitoring of aerosols, especially in the case of such hazardous volcanic events

A Backscatter Lidar Forward Operator for Particle-Representing Atmospheric Chemistry Models

“…The forward operator yields a lidar ratio for volcanic ash of between 15 sr and 80 sr which differs to lidar ratio values we find in literature (40 sr to 100 sr for volcanic ash (Kokkalis et al, 2013;Ansmann et al, 2010;Mortier et al, 2013)). This difference 5 may be a consequence of assuming spherical particles.…”

Development and application of a backscatter lidar forward operator for quantitative validation of aerosol dispersion models and future data assimilation

“…In the literature, we find measured lidar ratio values for volcanic ash between 40 sr and greater than 100 sr (Kokkalis et al, 2013;Mortier et al, 2013). This range of values could be observed within sensitivity studies of the pure lidar ratio (Sect.…”

Retrieval of the Eyjafjallajökull volcanic aerosol optical and microphysical properties from POLDER/PARASOL measurements

“…For the coarse mode of the volcanic plume, they found an effective radius of 1.28 µm, a real part of the refractive index of 1.51 (±0.05) with an imaginary part of 0.008 (±0.002) at 0.870 µm and a SSA of about 0.92 (±0.02) at 0.870 µm, which drops down to 0.81 (±0.02) at 0.44 µm. An increased real refractive index during the eruption time was also found in a study by Mortier et al (2013). Some retrievals made for the downwind case on 16 April (one day before the above-mentioned observations) also indicate high real refractive index values at some pixels; however, the retrievals do not show the same large absorption for this case.…”