Abstract
The anomalous variations in the vertical component (ΔZ) of the geomagnetic field have often been reported in many places of Japan. On the contrary, most of the authors except RIKITAKE (1965) and KUBOKI and OSHIMA (1965) have not paid attention to the distribution of the horizontal component (ΔR=√ΔH2+ΔD2) because marked differences have hitherto not been found in ΔR through Japan. However, surprisingly large ΔR compared with that at MEM (Fig. 1) was observed at some temporary stations in Hokkaido (NISHIDA, 1976, 1977a). For example, the ratio of ΔR at Hayakita, situated at the middle of the Ishikari Plain (Fig. 6), to that at MEM amounts to 1.8 in maximum though both stations are only about 240km apart. Therefore, it is greatly important to investigate the precise feature of the anomaly of ΔR amplitude. In this short note, the anomalies of ΔR amplitude in Hokkaido are discussed. Ahead of the discussions, the geomagnetic data at the permanent stations in the northeastern part of Japan and Sakhalin are analysed to examine the general tendency of ΔR amplitude in the region.
