Jónas Elíasson og Þorgeir Pálsson flytja erindi á málstofu Umhverfis- og byggingarverkfræðideildar Háskóla Íslands. Erindi þeirra ber heitið Airborne Measurements of Volcanic Ash and Current State of Ash Cloud Prediction.
Jónas Elíasson er rannsóknaprófessor við Rannsóknarmiðstöð Háskóla Íslands í jarðskjálftaverkfræði á Selfossi og prófessor við Disaster Prevention Research Institute (DPRI), Kyoto University í Japan.
Þorgeir Pálsson er prófessor við Háskólann í Reykjavík og fyrrverandi flugmálastjóri.
Ágrip
The Eyjafjallajökull 2010 and Grímsvötn 2011 eruptions created great problems for commercial aviation in North Atlantic and European airpace because of the large extent of the ash clouds that were predicted to emanate from these eruptions. Comparison to satellite pictures showed the predictions to be much larger than the actual ash cloud. Measurements also showed lower ash concentrations over Europe than had been predicted. Papers on the simulation of the Eyjafjallajökull Ash Cloud that appeared in peer reviewed journals typically emulated the predictions generated by the Volcanic Ash Advisory Center (VAAC) rather than the satellite images, an example of which is shown. In the most recent eruption in Iceland (Holuhraun – Bardarbunga 2014) mostly SO2 was produced. If its output had been in the form of volcanic ash, it could have produced similar problems for aviation as Eyjafjallajökull did in 2010. The plume was successfully modeled by Belgingur using the WRF-Chem model. Kyoto University measurements and research of eruptions in Sakurajima has shown weak points in the diffusion theory used for ash cloud prediction of tropospheric plumes that tend to ride in stable temperature inversions. Gravitational deformation of the plume and streak fallout processes are missing; both make estimated ash content of clouds, based on diffusion theory, larger than the actual. The dispersion coefficient in gravitational flattening is an order of magnitude smaller than is the case for diffusion. Streak fallout affects all grain sizes as it is a vertical flow of air. This makes airborne measurements of volcanic ash important as they provide calibration data for actual local source concentrations and grain sizes and thereby improve the predictions.
New ICAO procedures regarding air navigation , effective November 2014, state that the authority whether to avoid or proceed through a reported or forecast ash cloud rests with the pilot-in-command. ICAO also recommends that aircraft should avoid visible or discernable ash. This makes the detection of visible ash very important. Most VAAC’s use satellite imagery to localize visible ash clouds. The unique procedure used by JMA’s Tokyo VAAC is a good example whereby corrections of the modeled ash cloud based on satellite images ensure that predicted clouds are comparable to the observed ones in geopraphical extent. . Other VAAC´s are also pursuing similar approaches.
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