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Remote Sensing

EARLINET revealed four-dimensional distribution of volcanic ash

EARLINET performed almost continuous lidar measurements in April–May 2010 to follow the evolution of the volcanic plume generated by the eruption of the Eyjafjallajökull volcano.
29 November 2010, SPIE Newsroom. DOI: 10.1117/2.1201011.003289

Aerosols originating from volcanic emissions influence the climate and environment, and they could be dangerous to aircraft in flight. For this reason, the airspace over Europe was closed for several days during the latest eruption of Eyjafjallajökull volcano in April–May 2010.

Eyjafjallajökull is one of the smallest volcanoes in Iceland. An explosive eruption began around midnight on 14 April, and a volcanic plume was observed early in the morning of the same day. Eruptive activity continued almost without interruption until 24 May. Near the volcano, the resulting plume reached a variable maximum height (between 2 and 9km above sea level) during this period, which lasted for more than one month. Depending on the wind direction, the plume was transported toward different regions of continental Europe and the Atlantic Ocean at different altitudes.

Light detection and ranging (lidar) techniques represent an optimal tool for obtaining range-resolved data on volcanic ash plumes.1–3 EARLINET, the European Aerosol Research Lidar NETwork, established in 2000, is the first coordinated lidar network for tropospheric aerosol studies on a continental scale.4 Network activity consists of scheduled measurements, a rigorous quality assurance program addressing both the instruments and the evaluation algorithms, and a standard data exchange format.5–7 The network currently includes 27 lidar stations distributed over Europe as shown in Figure 1.

Figure 1. Map of lidar stations within EARLINET.

Soon after the explosive eruption of the Eyjafjallajökull volcano began, an alert was distributed to all EARLINET stations informing them about a large amount of ash directed toward northwestern Europe. Almost all of the stations made measurements whenever weather conditions permitted during the entire eruption. In response to both scientific and public interest in this volcanic eruption, EARLINET set up a web page where the public could access frequently updated views of lidar measurement data. In addition, a report containing all information concerning the EARLINET observations of volcanic ash was updated daily and made available online.8,9

EARLINET performed almost continuous measurements beginning 15 April 2010 to follow the evolution of the volcanic plume and determined its four-dimensional distribution over Europe. EARLINET was actually the only available observation system that could provide quantitative data about the presence, altitude, and layering of the volcanic cloud, together with optical information covering all of Europe. Moreover, its multi-wavelength lidar systems make it the only instrument worldwide that can provide both intensive and extensive optical data for use in aerosol typing and the retrieval of particle microphysical properties as a function of altitude.10–12

Intensive and extensive aerosol optical parameters derived from EARLINET observations have been used to characterize the particles originating in the eruption. During the first days, volcanic particles were detected over central Europe13 over a wide range of altitudes, from 12km down to the local planetary boundary layer. The time evolution of the volcanic cloud as observed by the EARLINET station in Munich on 16 and 17 April 2010 is shown in Figure 2 as an example. Until 19 April, transport of the plume toward southern Europe was almost completely blocked by the Alps. After that date, volcanic particles were detected over southern and southeastern Europe. On 20 April, the Italian EARLINET stations observed their first clear signatures of the plume. Part of the plume moved on and reached Greece on 21 April.

Figure 2. Time evolution of the volcanic cloud as observed by the EARLINET station in Munich on 16 and 17 April 2010. Left y-axis shows height in km; color indicates the log of the range-corrected lidar signal. (Courtesy of Matthias Wiegner, University of Munich.)

After a change in the main wind direction at the beginning of May, material emitted by the volcano reached western Europe using an almost direct path and was observed first over Spain and Portugal and then over Italy, Greece, and the Balkans. In this period, Saharan dust intrusions over southern Europe occurred as well, resulting in a very interesting aerosol situation in which volcanic and desert dust layers were present at different altitudes but in some cases also in a mixed-aerosol layer. The last observations of the event were recorded through 20 May in central Europe and the eastern Mediterranean.

These observations represent an unprecedented data set for evaluating satellite data and aerosol dispersion models and can be used as a reference for observations at global scale.

The financial support of the European Commission under grant RICA-025991 is gratefully acknowledged. Special acknowledgment is also given to all the EARLINET staff who worked hard day and night to follow the volcanic event.

Gelsomina Pappalardo
National Research Council,Institute of Methodologies for Environmental Analysis
Tito Scalo (Potenza), Italy

Gelsomina Pappalardo is a physicist whose primary research interests include lidar remote sensing of aerosols, clouds, and water vapor. She is the EARLINET speaker and the coordinator of the EARLINET Advanced Sustainable Observation System project of the European Commission Sixth Framework Program.