In May 2010, the ash cloud from the Icelandic volcanoEyjafjallajokull reached the Iberian Peninsula and brought airportsto a halt all over Europe. At the time, scientists followed itspaths using satellites, laser detectors, sun photometers and otherinstruments. Two years later they have now presented the resultsand models that will help to prevent the consequences of suchnatural phenomena. The eruption of the Eyjafjallajokull in the south of Iceland beganon the 20 March, 2010. On the 14 April it began to emit a cloud ofash that moved towards Northern and Central Europe, resulting inthe closure of airspace. |
Hundreds of planes and millions ofpassengers were grounded. After a period of calm, volcanic activity intensified once again onthe 3 May. This time the winds transported the aerosols (a mixtureof particles and gas) towards Spain and Portugal where someairports had to close between the 6 and 12 May. This was also abusy time for scientists who took advantage of the situation tomonitor the phenomenon.
Their work has now been published in theAtmospheric Environment journal. "The huge economic impact of this event shows the need to describewith precision how a volcanic plume spreads through the atmosphere.It also highlighted the importance of characterising in detail itsparticles composition and establishing its concentration limits toensure safe air navigation," explains Arantxa Revuelta, researcherat the Spanish Research Centre for Energy, Environment andTechnology (CIEMAT). The team identified the volcanic ash cloud as it passed over Madridthanks to LIDAR (Light Detection and Ranging), the most effectivesystem for assessing aerosol concentration at a height. The CIEMATstation is one of 27 belonging to the European network EARLINET(European Aerosol Research Lidar Network) that use this instrument.Its members have also published a publicly accessible article onthe matter in the Atmospheric Chemistry and Physics journal.
Using LIDAR technology, scientists direct a laser beam towards thesky, like a saber in Star Wars. The signal reflected back fromparticles provides information on their physical and chemicalproperties. A maximum aerosol value of 77 micrograms/m3 wasestimated, which as a concentration is below the risk valueestablished for air navigation (2 miligrams/m3). Furthermore, the levels of particles rich in sulphates shot up eventhough they were fine particles (with a minimum diameter of 1micra).
This meant that they were much smaller than those particlesover 20 micra found in countries in Central Europe. These thicker particles are generally considered to be 'ash' andcan really damage aircraft motors. The fine matter, like thatdetected over the Iberian Peninsula, is similar to that commonlyfound in urban and industrial areas. It is subject to study morefor its damaging health effects rather than its impact on airnavigation.
NASA's network of sun photometers It is important to track the evolution of all the particles inorder to provide information to managers responsible for this kindof crisis. Working in this field were members of NASA's AERONET(AErosol RObotic NETwork) network, which is made up by thedifferent tracking stations in Spain and Portugal (integrated intoRIMA) equipped with automatic sun photometers. These instrumentsfocus towards the sun and collect data each hour on the aerosoloptical thickness and their distribution by size in the atmosphericcolumn. The combined use of sun photometers and LIDAR technology boostsdata collection.
For example, the station in Granada and Evorarevealed that the volcanic ash cloud circulated between 3 km and 6km above the ground. "Instruments like LIDAR are more powerful on an analytical levelbut their spatial and weather coverage is low. This means that sunphotometers come in very useful in identifying volcanic aerosolswhen no other measures are available," outlines the researcherCarlos Toledano from the University of Valladolid and member of theAERONET-RIMA network. From their stations it was confirmed that "there is great variationbetween the size and characteristics of the volcanic aerosolparticles over successive periods." This was also verified by members of another European Network, EMEP(European Monitoring and Evaluation Program), which tracesatmospheric pollution and is managed in Spain by the NationalMeteorological Agency.
This group confirmed an increase in aerosolsand their sulphate concentrations over the Iberian Peninsula andrecorded the presence of sulphur dioxide from the Icelandicvolcano. Models and Predictions The large part of observations of Eyjafjallajokull's eruption,which were taken from aeroplanes, satellites or from earth, helpedscientists validate their prediction and particle dispersionmodels. "During the management of the crisis it became evident that thereare still no precise models that provide real time data fordelimiting an affected airspace, for example," admits Toledano. Nevertheless, his team put the FLEXPART model to test usingempirical data. From the Norwegian Institute for Air Research(NILU), it managed to calculate the arrival of volcanic ash incertain situations.
The powerful equipment available at the Barcelona SupercomputingCenter (BSC-CNS) was used on this occasion to validate a modelwhich had been developed at the centre: the Fall3d. As one of the authors Arnau Folch states, "the model can be appliedto the dispersion of any type of particle. But, in practice, it hasbeen especially designed for particles of volcanic origin, likeash." Volcanologists and metereologists use this model to re-enact pastevents and, above all, to make predictions. More specifically itpredicts the amount of aerosols in the ground and theirconcentration in the air. It is therefore of "special interest" to civil aviation.
The finalobjective is to make this type of prediction so as to be preparedduring the next volcanic eruption. References: "Characterization of the Eyjafjallajokull volcanicplume over the Iberian Peninsula by lidar remote sensing andground-level data collection". A. Folch, A.
Costa, S. Basart:"Validation of the FALL3D ash dispersion model using observationsof the 2010 Eyjafjallajokull volcanic ash clouds". AtmosphericEnvironment 48: 22-32/46-55/165-183, March 2012. M.
Sicard, J. L. Guerrero-Rascado, F. Navas-Guzman, J. Preibler, F.Molero, S.
Tomass, J. A. Bravo-Aranda, A. Comeron, F.
Rocadenbosch,F. Wagner, M. Pujadas, L. Alados-Arboledas. "Monitoring of theEyjafjallaj'okull volcanic aerosol plume over the Iberian Peninsulaby means of four EARLINET lidar stations".
Atmospheric Chemistryand Physics 12: 3115-3130, 2012. DOI:10.5194/acp-12-3115-2012.
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