Seasonal Variations of Sq Current System in Different Longitudinal Sectors and Solar Activities

Years of geomagnetic observatory data during the geomagnetic quiet days (Kp <= 3) at the low and middle dip latitudes from INTERMAGNET and SuperMAG were utilized. Seasonal models of Sq currents for two longitudinal chains at each year and under two solar activity levels (F10.7 index are similar to 75 and 125 sfu) were constructed by spherical harmonic analysis. It is found that there are significant seasonal variations of Sq currents in the Asian-Oceanian (A-O) and North-South American (N-SA) longitude sectors under different solar activities. First, the focus intensity J increases faster in local winter than in summer for both two hemispheres as solar activity strengthens. J of ionospheric currents in the northern hemisphere (NH) during local winter is higher than that in the southern hemisphere during its winter. This asymmetric activity in the N-SA chain increases with the solar activity becomes stronger. Second, with solar activity increases, the ionospheric current focus of N-SA chain in the NH shifts toward the lower latitudes during two solstices, while internal current focus of both two chains move toward the lower latitudes during the December solstice. Seasonal variations of Sq currents in the two chains exhibit longitudinal effects. With increasing solar activity, the two hemispheric focuses of the ionospheric currents in the A-O chain both move closer to the midday longitude sector, while in the N-SA chain, only the focus in the NH shifts toward noon. The results reveal details of the seasonal variations of Sq currents. Seasonal models of Sq currents at low and middle latitudes were constructed by spherical harmonic analysis in two longitudinal chainsThe characteristics of the seasonal variations and their dependence on solar activity for the A-O and North-South American chains were obtainedThe longitudinal effects of the seasonal variations in Sq currents were revealed