核磁力計による桜島磁場観測 (2)

Abstract

The purpose of this paper is the descriptions of the variations of daily mean values of geo-magnetic total intensity at night-time (22-04h JST) observed with proton precession magnetometersat Kurokami and Furusato being situated in Sakurajima volcanic island, from January, 1976, tillJune, 1977.A number of variations in the total intensity that might be related to the volcanic activitywere observed.The data, 1976, were examined mutually and were compared with the values of Kanoyageomagnetic permanent station. The following results are obtained. In the active period oneruptions of Sakurajima volcano, the increment or decrement of anomalous field changes of 2gammas were observed at Kurokami. On the assumption that no local geomagnetic disturbancesexisted at Kanoya, the gradual change of -2 gammas had existed at Kurokami from January toJune, while the field at Furusato had been steady in those months. Since July, 1976, the incrementhad appeared to the end of the year at Kurokami but the decrement had occurred at Furusato.Examining the data, 1977, at Kanoya by means of the weighted difference method with thevalues at Aso and Yoshimatsu, it was found out the field was varied at Kanoya locally but wassteady at Yoshimatsu. Then the data, 1977, at Kurokami and Furusato were compared with thevalues of Yoshimatsu. The results showed that the gradual decrement of the total intensity of1.5-2 gammas was recognized at Kurokami and Furusato in the first half 1977.