[O-08] Poster presentations by senior high school students

[O08-P01] Research in the amount of ash fall on Sakurajima Volcano and seasonal fluctuations in the wind direction

*Yuka Matsuo¹, *Tadahiro Ishizaki¹, *Yuzuki Kashiwagi¹, Koharu Furukawa¹, Kazuki Tajima¹, Kichinosuke Sameshima¹, Haruto Mizuno¹ (1.Kokubu High School)

Keywords:Sakurajima Volcano, volcanic ash, Ekman spiral, Monsoon

In Kagoshima, it is a daily routine to check the ash fall forecast associated with the eruption of Sakurajima. When Sakurajima erupts, the released volcanic ash is thought to flow downwind and accumulate due to the wind. I was curious if the volcanic ash was actually flowing downwind. When the relationship between the ash flow direction of Sakurajima and the average wind of 1500 m above the sky was investigated, the average wind in the sky was shifted to the right by about 45 degrees with respect to the direction of the ash flow direction. This turned out to be the same tendency as Ekman's blow stream. Therefore, I decided to investigate whether such a deviation can be seen even if the conditions are further increased. We also decided to investigate whether there was a change in the wind direction due to abnormal weather. The movement that occurs when the turning force of the earth's rotation (Coriolis force) and the frictional force that drags the lower layer of seawater work is called Ekman's blowing flow. In the northern hemisphere, the surface current shifts 45 degrees to the right (45 degrees to the left in the southern hemisphere) with respect to a certain wind direction. Although there is a difference of 1000m in altitude, there was a difference between the ash flow direction and the wind direction over Sakurajima in both January-May, September-December and June-August. At an altitude of 2600m, it was confirmed that both periods were shifted to the right by about 45 degrees. Even if the conditions are increased, there is a gap between the ash flow direction and the wind direction in the sky, so it is possible that the rotation of the earth has an effect even in the sky. Ash flows in the southeast direction from January to May, from September to December, and in the east direction from June to August. In both periods, there was a discrepancy between the ash flow direction and the wind direction in the sky. At an altitude of 2600m, it was confirmed that it was shifted to the right by about 45 degrees. In the future, the conditions will be further increased, and it was found that there is a regular deviation (Ekman spiral) between the wind and ash flow in the sky due to the difference in the eruption altitude. Using the Foucault pendulum experimental device, it was possible to confirm in the laboratory experiment that the Coriolis force was actually working. In the future, I would like to investigate whether there is a change in the wind direction that indicates abnormal weather from the data of the meteorological observatory. Also, I would like to obtain the volcanic ash of Sakurajima collected by the Kagoshima prefectural government and investigate the mineral composition and particle size. In addition, we would like to actually collect the ash immediately after the eruption of Sakurajima and analyze the particle size and mineral composition of the volcanic ash.