Effect of the non-dipole field on the seasonal variation of the
geomagnetic Sq(Y)
Abstract
Different timescales of the daily amplitude of the geomagnetic Y
component during quiet period (Sq(Y)) over several solar cycles at 25
mid-low latitudes observatories were analyzed. The annual mean
(Sq0), annual (Sq1) and semiannual
(Sq2) components were separated from Sq(Y) by means of
Fourier analysis method. 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. Sq1(Y) exhibits a remarkable
longitudinal inequality, which is much stronger around Eurasia and
Australia anomaly zones and weaker around South Atlantic Ocean anomaly
zones. The positive correlation between Sq0(Y) and
geomagnetic vertical component Z suggests that the convection
electric fields in the dynamo region play a key role in controlling
annual mean (Sq0). On the other hand, the
Sq1(Y) exhibits a positive correlation with geomagnetic
horizontal component H, implying the inter-hemispheric
field-aligned currents (IHFACs) may contribute to difference of the
annual variation amplitude at different observatories. The
Sq2(Y) is most prominent in the South Atlantic Ocean
anomaly (SAO) region. It is possible the stronger ionospheric
conductivity in the dynamo region contribute to the remarkable
semiannual variation at SAO region.