Contribution of wind, conductivity, and geomagnetic main field to the variation in the geomagnetic Sq field

摘要

abstract_textpLong-term variation in the geomagnetic Sq field and the cause of the variation were examined. The amplitude of the geomagnetic Y component (Sq(Y)) in equinox was averaged for each year and adopted as a proxy of the Sq field. Sq(Y) was combined with the ionospheric conductivity estimated by the International Reference Ionosphere model to determine the dynamo electric field and neutral wind velocity by using the geomagnetic main field strength. It was found that the solar activity dependence of the Sq field could be almost completely attributed to the conductivity variation, and neutral winds tend to decrease when the solar activity increases. Although the long-term variation in the dynamo field differed among observatories, these differences were mostly attributed to the locality of the geomagnetic secular variation, whereas the variations in neutral wind amplitude were nearly the same in all regions. On the other hand, no clear long-term variation in neutral wind was detected other than that by solar activity./p/abstract_text