On the Residual Part of the Geomagnetic Sq-Field in the Middle and Lower Latitudes during the International Polar Year, 1932-33

A detailed spherical harmonic analysis of the Sq-field shows that this field contains not only terms depending on local time but fairly conspicuous residual terms. These residual terms seem to arise mainly from an effect of the discrepancy between the earth's magnetic and rotational exec upon the dynamo-action in the Sq-layer.By coordinate transformation to make the residuals least, we get a more suitable coordinate for the Sq-field than the geomagnetic one.