UT and day-to-day variations in equivalent current systems for world geomagnetic variations.

Equivalent current systems of the daily geomagnetic variations are drawn for every two hours throughout the month, December 1964, to investigate universal-time (UT) and day-to-day variations in the middle and low latitude regions. It is confirmed that there co-exist two types of UT variations in the current systems, the regular and the occasional ones. It is also found that the UT variations in the intensities of the northern and southern current vortices are generally in the opposite sense for both the external and internal current systems, though they are sometimes in the same sense. The centers of the northern and southern vortices move in the same direction, coming most northwards at about 10-12h UT and most southwards at about 02-04h UT. The harmonic coefficients of the geomagnetic variation show a periodic change with UT, in accordance with the regular UT-dependence of Sq on quiet days. The day-to-day changes at fixed UT's in the intensity and position of the current systems depend systematically on UT. These and other results obtained are discussed in relation to the origin of the regular and occasional variations in the equivalent current systems.

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