Abstract
The problem of dynamo action of tidal stream or ocean current in the earth's magnetic field has a long history of research. I investigated the effect of magnetic field induced by this action on geomagnetic observations. This problem seems very important to assure the accuracy of geomagnetic observations, because Japan islands are surrounded by sea and high speed ocean currents such as Kuroshio and Oyashio flows. The vertical component observed at Shimosato shows a remarkable seasonal variation. The relation between this phenomena and Kuroshio has been expected to be its origin. I calculated the induced magnetic field for a simple model of ocean current which flows straight with semi-elliptic cross section. This field is restricted in water and amounts to about 37 r/knot in magnitude. However, possible leakage of flux of this field which approaches near peninsura or encounters island is so small that ordinary magnetic measurement on land is not practically influenced. Seasonal variation at Shimosato can hardly be explained by this line of thought. The magnetometer in water may be disturbed by this induced field to the order of ten gammas according to circumstances. We may obtain information about the path of ocean current to a certain degree, with a suitable distribution of magnetometers in water.
