【Notes】Geomagnetic total intensity observations at Izu-Oshima volcano - causes of the observed data variations -
Masahiro SASAOKA
Abstract
Kakioka Magnetic Observatory has been monitoring the volcanic activity of Izu-Oshima by performing continuous observations of geomagnetic total intensity north of Miharayama crater on Izu-Oshima at two Mihara-Kita sites (MIK1 and MIK2). The differences in long-term trends between the observed geomagnetic total intensity and secular variation were examined by comparing data from the two Mihara-Kita sites during 2007-2013 with reference site data (Kakioka and Kanoya). The geomagnetic variation at MIK1 was similar to the secular variation, but the variation at MIK2 was considerably greater than that at the reference sites. The geomagnetic variations observed at MIK1 and MIK2 are out of phase with magnetization changes at the crater, which reflects the low level of volcanic activity at Izu-Oshima at present. The nighttime and daily averages of total geomagnetic intensity at MIK1 and MIK2 correspond to the Dst (disturbance storm time) index variations; thus, the geomagnetic variations at the two sites consist of the residual components of the external magnetic field and reflect seasonal variations of solar activity with a six-month period.
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