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Abstract:
The annual mean (Sq0), annual (Sq1), and semiannual (Sq2) components of the monthly averageddaily amplitude of the geomagnetic Y component during quiet period over several solar cycles at 25 mid-lowlatitudes observatories were separated by means of Fourier analysis. No obvious distinction is found for themorphology of the spatial distribution of these Sq(Y) components during solar quiet and active periods, exceptthat they are more intense in high solar activity. We found that the longitudinal variations in the SouthernHemisphere were primarily attributed to the differences in the annual component (Sq1), which is stronger atthe Eurasia and Australia anomaly zones than at the South Atlantic Ocean anomaly (SAA) zones. The positivecorrelation between Sq0 and geomagnetic vertical component Z suggests that the convection electric fields inthe dynamo region play a key role in controlling the annual mean (Sq0). On the other hand, the Sq1 exhibits apositive correlation with geomagnetic horizontal component H, implying the interhemispheric field-alignedcurrents (IHFACs) may contribute to difference of the annual variation amplitude at the different observatories.Sq2 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.
