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This work describes the month‐by‐month behavior of the equivalent ionospheric current systems derived from spherical harmonic analyses of the quiet time geomagnetic field daily variations in 1965 at selected observatories representing the three southern global half‐sector regions separately encompassing South America, Africa, and Australia. These external Sq current patterns were vortices having mid‐latitude foci with midday summertime amplitudes reaching 16.2×10 4 A above the midnight level. The wintertime amplitudes were about 10×10 4 A smaller. At low latitudes there was a large intrusion of the opposite hemisphere external Sq current system into the wintertime hemisphere at prenoon hours, displacing the primary current vortex to later postnoon hours. The behavior of the southern hemisphere external currents were found to be seasonally similar to those of the northern hemisphere for the same year. The quiet year behavior was compared to the results for the 1958 active year determined earlier by Matsushita. The winter‐to‐summertime increase in focus current was found to be similar in amplitude for the 2 years. The active year summertime and equinoctial current focus amplitudes were about 2.3 times the amplitudes of corresponding months in the quiet year.
Campbell et al. (Mon,) studied this question.