@inproceedings{EliassonPalssonWeber2017, author = {Eliasson, Jonas and Palsson, Thorgeir and Weber, Konradin}, title = {State of volcanic ash dispersion prediction}, series = {Geophysical Research Abstracts: EGU General Assembly 2017}, booktitle = {Geophysical Research Abstracts: EGU General Assembly 2017}, publisher = {Copernicus}, address = {G{\"o}ttingen}, year = {2017}, abstract = {The Eyjafjallajokull 2010 and Grimsvotn 2011 eruptions created great problems for commercial aviation in Western Europe and in the North Atlantic region. Comparison of satellite images of the visible and predicted ash clouds showed the VAAC prediction to be much larger than the actual ash clouds. No official explanation of this discrepancy exists apart from the definition of the ash cloud boundary. Papers on simulation of the Eyjafjallaj{\"o}kull ash cloud in peer reviewed journals, typically attempted to simulate the VAAC predictions rather than focusing on the satellite pictures. Sporadic measurements made in-situ showed much lower ash concentrations over Europe than the predicted values. Two of the weak points in ash cloud prediction have been studied in airborne measurements of volcanic ash by the Universities in Kyoto Japan, Iceland and D{\"u}sseldorf Germany of eruptions in Sakurajima, Japan. It turns out that gravitational deformation of the plume and a streak fallout process make estimated ash content of clouds larger than the actual, both features are not included in the simulation model. Tropospheric plumes tend to ride in stable inversions this causes gravitational flattening (pancaking) of the volcanic plume, while diffusion in the mixing layer is insignificant. New rules from ICAO, effective from November 2014, reiterate that jetliners should avoid visible ash, this makes information on visible ash important. A procedure developed by JMA′s Tokyo VAAC uses satellite images of visible ash to correct the prediction. This and the fact that meteorological data necessary to model gravitational dispersion and streak fallout do not exist in the international database available to the VAAC′s. This shows that close monitoring by airborne measurements and satellite and other photographic surveillance is necessary.}, subject = {Vulkanismus}, language = {en} } @inproceedings{WeberFischerLangeetal.2017, author = {Weber, Konradin and Fischer, Christian and Lange, Martin and Schulz, Uwe and Naraparaju, Ravisankar and Kramer, Dietmar}, title = {Design and construction of a testbed for the application of real volcanic ash from the Eyjafjallaj{\"o}kull and Grimsv{\"o}tn eruptions to microgas turbines}, series = {Geophysical Research Abstracts: EGU General Assembly 2017}, volume = {19}, booktitle = {Geophysical Research Abstracts: EGU General Assembly 2017}, publisher = {Copernicus}, address = {G{\"o}ttingen}, year = {2017}, abstract = {It is well known that volcanic ash clouds emitted from erupting volcanoes pose a considerable threat to the aviation. The volcanic ash particles can damage the turbine blades and their thermal barrier coatings as well as the bearings of the turbine. For a detailed investigation of this damaging effect a testbed was designed and constructed, which allowed to study the damaging effects of real volcanic ash to an especially for these investigations modified microgas turbine. The use of this microgas turbine had the advantage that it delivers near reality conditions, using kerosene and operating at similar temperatures as big turbines, but at a very cost effective level. The testbed consisted out of a disperser for the real volcanic ash and all the equipment needed to control the micro gas turbine. Moreover, in front and behind the microgas turbine the concentration and the distribution of the volcanic ash were measured online by optical particle counters (OPCs). The particle concentration and size distribution of the volcanic ash particles in the intake in front of the microgas turbine was measured by an optical particle counter (OPC) combined with an isokinetic intake. Behind the microgas turbine in the exhaust gas additionally to the measurement with a second OPC ash particles were caught with an impactor, in order to enable the later analysis with an electron microscope concerning the morphology to verify possible melting processes of the ash particles. This testbed is of high importance as it allows detailed investigations of the impact of volcanic ash to jet turbines and appropriate countermeasures.}, subject = {Vulkanismus}, language = {en} }