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While the plume height ranged from 3 to 10 km, we will simulate Eyjafjallajokul using use its average plume height of 7.3 km for our simulations of Eyjafjallajokul.
Source: NASA, https://www.nasa.gov/topics/earth/features/iceland-volcano-plume-archive1.html
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HYSPLIT Simulations for Eyjafjallajokull (Varying Eruption Date)
The simulations will be computed using HYSPLIT (https://www.arl.noaa.gov/hysplit/hysplit/), a model developed by the National Oceanic and Atmospheric Administration (NOAA)'s Air Resources Laboratory. The model is used for tracer transport and computes air parcel trajectories; it is similar to ESGlobe, which we used in Project II. Its computational approach employs a combination of the Lagrangian and Eulerian methodologies. The Lagrangian approach uses a frame of reference that moves with the air parcels and the Eulerian approach uses a fixed 3D frame of reference.
Although the eruptions contributing to the majority of ash fall lasted for 6 days, the simulations will cover the first three days of eruptions.
April 14-16, 2010
First we I will simulate the eruption on its actual eruption date of April 14th. We I will also examine the constant pressure surface for an atmospheric pressure of 500 mb on the second day of the eruption in order to determine if the dispersal followed the expected wind patterns.
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Image 3: Shows the constant pressure surface for 500 mb on the second day of the eruption. The contour lines illustrate the wind patterns for horizontal wind flows on a constant pressure surface. Black The coriolis force balances the pressure gradient, and thus the flow follows the constant pressure lines. Black arrows illustrate the relevant flows around Iceland. The winds move eastward towards England and then south. They also move north-westwards.
Simulation of Particle Positions for April 14-16 Eruption
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Image 4: 3-day ash dispersal simulation for Eyjafjallajokull for actual eruption date of April 14, 2010. The plume initially moves north-eastward and then south-westard. As the plume moves northward it deflects to the east and as it moves southward it deflects to the west as predicted by the rightward deflection of the coriolis force in the northern hemisphere. The two layers closest to the Earth's surface spread the furthest.
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Image 5: 3-day Ash dispersal by arrival time for Eyjafjallajokull for actual eruption date of April 14, 2010. The ash reaches the eastward regions.
We I will now simulate the ash dispersal for if the eruption occurred a week earlier. We I hope to establish a sense of the magnitude of weekly variations in ash dispersal before examining the dispersal for the eruption in different seasons.
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Image 7: 3-day Ash dispersal by arrival time for Eyjafjallajokull for eruption date of April 7, 2010. The ash reaches Europe and encircles the north pole.
We I will now simulate the eruption in January to investigate how the dispersion changes by season–specifically in the winter when the equator-pole temperature gradient peaks. We I hope to determine if the variation by season exceeds that by week and if so, the patterns that characterize winter ash dispersal.
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Image 9: 3-day Ash dispersal by arrival time for Eyjafjallajokull for eruption date of April January 1, 2010. The ash spreads in a circle around Iceland and reaches both the U.S. and Europe.
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The ash dispersal by plume arrival images for the eruptions from January 1-3 and from January 8-10 do not exhibit any prominent similarities–the dispersal in the first week of January forms a circle around Iceland whereas in the second week it moves only northeast and southeast in separate streams. Thus we cannot identify any large scale trends for the January dispersals.
We Next I will not look at simulations for the warmer month of July. We would I anticipate that the ash will disperse over a smaller area in July for the lower temperature gradient should result in slower zonal winds.
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Image 14: 3-day Ash dispersal by arrival time for Eyjafjallajokull for eruption date from July 8-10, 2010. The ash forms plume initially moves southeastward and then begins to spiral counter-clockwise towards the pole. The counter-clockwise motion towards the pole confirms theoretical predictions about that due to the effect of the coriolis force at higher latitudes, the flow would move counter-clockwise like the Earth's rotation. In the final day, the ends of the plume deflect eastward. They ; the ends may have been caught in eddy cells.
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Similar to those for January, the two July simulations did not demonstrate any major similarities. I did not identify any dispersal trend for July. trends for July. Moreover, the areas spanned by the ash did not noticeably differ in the January versus July simulations–despite my prediction that the more extreme temperature gradient in the winter would lead to a larger covered area due to higher zonal winds.
Conclusions
By simulating Eyjafjallajokull for various eruption dates, I had sought to investigate how the circulation patterns changed both seasonally and weekly and whether the seasonal versus weakly variations dominated the ash dispersal patterns. Simulations showed that the weekly changes in atmospheric circulation patterns dominated any seasonal trends. Eyjafjallajokull sits at the boundary between two different air masses (between the polar and eddy regimes--air nearer to the poles is generally cold and dry whereas at mid-latitudes it is warmer and also influenced by the tropics). This region is influenced by the North Atlantic Oscillation (NAO) phenomenon in which the circulation patterns vary dramatically.
The pronounced weekly variation in the ash dispersal may result from the varying eddies that pass by the region of the volcano. The eddies are mesoscale (order of 1000 km), and thus which eddy occupies the region during the eruption would likely function as the main determinant of the ashes' dispersal. Moreover, the local variance has significant downstream effects. In simulation for the eruption on January 1, 2010, the ash reached the U.S. whereas in the simulation a week later on January 8, 2010, the ash reached Russia.
Our The simulations also give us insights into our record of past volcanoes. We often research past volcanoes through the ash they deposited in Greenland ice cores. Given that in many of our simulations the ash from our Icelandic volcano did not reach its neighboring country, we may likely lack eruption recordings for many past local volcanoes near Greenland.
Next Steps
My simulations did not demonstrate seasonal trends; in order to demonstrate seasonal trends, one should take the daily average of all dispersal simulations over the month of January versus the daily average over the month of July. Due to the daily variations, looking at individual days in January versus individual days in July did not show meaningful insights re seasonal trends.
It would also be interesting to look at the In order to understand the smallest time period over which changing the eruption date would cause the ash dispersal to vary. To do so, one must look into the time scales of the eddys in the Icelandic region. Further simulations should explore variations in dispersal from daily changes to the eruption date . (as opposed to daily averages over month-long periods to see seasonal trends).