Quiet ionospheric currents of the northern hemisphere derived from geomagnetic field records

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Abstract
A special selection of extremely quiet 1965 geomagnetic daily variation records from North America, Europe, central Asia, and east Asia was used to determine monthly spherical harmonic analysis coefficients representing the Sq fields from these regions. The coefficients permitted a separation of the external and internal contributions to the daily variations. Month‐by‐month behavior of the equivalent external current system and contours of the daily range of this current showed regional differences in amplitude and location of the equivalent ionospheric currents with seasonal change. Current foci locations reached 35° to 42° geomagnetic latitude in summer and 18° to 35° in winter with a regional dependence. The largest daily range of external current was 14.6×104 A in North America, 15.3×104 A in Europe, 13.7×104 A in central Asia, and 12.3×104 A in east Asia. Continental differences in the behavior of the current seemed to be explained by the relative position of the geographic and geomagnetic poles with respect to these regions.