Effect of the Non-Dipole Field on the Seasonal Variation of the Geomagnetic Sq(Y)

The annual mean (Sq(0)), annual (Sq(1)), and semiannual (Sq(2)) components of the monthly averaged daily amplitude of the geomagnetic Y component during quiet period over several solar cycles at 25 mid-low latitudes observatories were separated by means of Fourier analysis. No obvious distinction is found for the morphology of the spatial distribution of these Sq(Y) components during solar quiet and active periods, except that they are more intense in high solar activity. We found that the longitudinal variations in the Southern Hemisphere were primarily attributed to the differences in the annual component (Sq(1)), which is stronger at the Eurasia and Australia anomaly zones than at the South Atlantic Ocean anomaly (SAA) zones. The positive correlation between Sq(0) and geomagnetic vertical component Z suggests that the convection electric fields in the dynamo region play a key role in controlling the annual mean (Sq(0)). On the other hand, the Sq(1) exhibits a positive correlation with geomagnetic horizontal component H, implying the interhemispheric field-aligned currents (IHFACs) may contribute to difference of the annual variation amplitude at the different observatories. Sq(2) is most prominent in the SAA region while rather weak at other positive anomaly zones (in total field), which indicates there is a negative correlation between the total field anomaly and the semiannual variations.