Ionospheric disturbance excited by the 2015 Kuchinoerabu-jima, southwest Japan, eruption

Abstract:

Vertical displacements excited by volcanic eruptions, earthquakes, or tsunamis excites pressure waves in the atmosphere. The excited oscillation propagates to ionosphere where solar radiation ionize a part of atmosphere, resulting in a disturbance of the total electron content (TEC).

Where numerous studies have reported ionospheric disturbance excited by earthquakes or tsunamis, much smaller number of studies have investigated that excited by volcanic eruptions. This study reports on the ionospheric disturbance excited by the 2015 Kuchinoerabu-jima eruption observed by continuous GPS observations.

The 2015 Kuchinoerabu-jima eruption is a phreatomagmatic eruption occurred on 29 May 2015. The eruption is explosive with a column height up to 10,000 meters above the vent. The disturbance of TEC started from about 10 minutes after the eruption at approximately 100 km from the volcano. The disturbance then propagates outward for about 10 minutes. The velocity of pressure wave is estimated to be about 500 m/s, consistent with the average acoustic velocity in the ionosphere.

The dominant frequency of the observed disturbance is about 11 mHz, much higher than the eigenfrequencies of Earth's atmosphere, 3.7 mHz and 4.4 mHz. The dominant frequency observed here might be related to the dominant frequency of the acoustic wave excited by the eruption and the dissipation of the medium.

While the ionospheric disturbance associated with the 2003 Soufrière Hills lasted more than an hour, that in this study lasted only up to a few minutes. This difference might correspond to the difference in time scale of the excitation.

The pressure wave excited by the eruption is also recorded by broadband seismometers in the Japanese islands. Our goal is thus to gain more insights into the mechanics of lithosphere-atmosphere-ionosphere coupling as well that of the 2015 Kuchinoerabu-jima eruption consisent with both seismic and GPS observations.