Difference in seasonal and long‐term variations in geomagnetic Sq fields between geomagnetic Y and Z components

Abstract

The amplitudes of geomagnetic solar quiet (Sq) fields in the Y (Sq(Y)) and Z (Sq(Z)) components were examined by the data obtained from several observatories for a period of more than 50 years. It was found that both Sq(Y) and Sq(Z) are strongly influenced by the solar activity and correlate fairly well with each other during all seasons. However, their seasonal variations are different. This is probably because Sq(Y) and Sq(Z) reflect the current intensity at different UTs, and different seasonal variations at different UTs lead to the difference in the seasonal variation of Sq(Y) and Sq(Z). The ratio of Sq(Z) to Sq(Y) is larger in winter than in summer at all observatories except for those in high geomagnetic latitudes. This difference is superficially attributed to the variation of the equivalent Sq current system, and probably significant part of the variation is due to interhemispheric field‐aligned currents driven by the Sq dynamo. On the other hand, long‐term variation in Sq(Z) at Honolulu was affected by the movement of the observatory in 1960, which illustrates the importance of induced currents in the ocean for the Sq field in the Z component.