The latitudinal asymmetry of the seasonal variation of the amplitude of the Sq field

The geomagnetic field shows a regular diunal variation at the middle and low latitudes during geomagnetic quiet time, which is called as solar quiet daily variation (Sq). It is mainly generated from the ionosphere dynamic current system in the E-region of ionosphere, which is controlled by the ionospheric diunal and semi-diunal tidal wind field. The variation of the Sq field is greatly related to the latitude and the local time, and its amplitude and the phase vary very slowly in the whole year. Furthermore, a significant day-to-day (DTD) variation is usually seen in the amplitude and the phase of the Sq. It is greatly related to many factors such as the conductivity and the wind field in the ionosphere, and states of the magnetosphere.

This work is primarily to investigate the seasonal variation of the amplitude of the Sq field on both north-and-south sides of the Sq current, by using of the hourly data of the geomagnetic horizontal field from 75 observatories at mid-and-low latitudes. The result indicates that there is a significant seasonal variation in the amplitude of Sq(H) at all observatories, which shows a great enhancement during equinoxes months. However, a notable latitudinal asymmetry is clearly seen between the northside and southside observatories. The amplitude of Sq(H) reaches the maximum value in autumn at northside observatories, but in spring at southside observatories. This latitudinal asymmetry is most likely to reflect the tilt of the ionosphere current vortex.