核磁力計による桜島磁場観測 (1)

Abstract

The observations of geomagnetic total intensity have been conducted with a proton precessionmagnetometer since January 1975 at Kurokami on Sakurajima volcanic island. The data wereanalyzed with reference to Kanoya Geomagnetic Observatory which was situated 25 km southeast ofSakurajima. The following results are obtained.Bay type geomagnetic disturbances which have the period of 1 to 2 hours were smaller thanabout 2γ those at Kanoya. In the case of longer period, the changes at Kurokami were smallerthan the Kanoya changes at night, though the Kurokami changes were equal or a bit great indaytime.The differences of the daily mean values at night-time between the two stations were nearlyequal, though the 1-2γ undulatory fluctuations of the period of 10 to 40 days were seen. Thenthe values of geomagnetic survey on Sakurajima which are reduced to Kanoya will include theerror of the amounts of 2-3γ nonlocal geomagnetic changes.Remarkable local geomagnetic changes have not been found out at Kurokami in connectionwith the volcanic activities of Sakurajima in the duration of January to October in 1975.