Seasonal and day-to-day changes of the central position of theSqoverhead current system

Abstract

The solar daily geomagnetic variation on quiet days, Sq, is due mainly to the overhead electric current system flowing in the lower ionosphere. Figure 1 gives the well-known diagrams of the Sq overhead current system in two seasons, obtained by Bartels [Bartels, 1928; Chapman and Bartels, 1940] from spherical harmonic analysis of geomagnetic data obtained at 18 stations in the sunspot-minimum year 1902. The overhead current system consists of four sets of ovals, two each in the northern and southern hemispheres. In the present study the position of the center of the current system— that is, the location of the focus of a counterclockwise oval current—for the daylight hours in the northern hemisphere was found to undergo a remarkable seasonal change. The center, on the average, was found to be in higher latitudes in summer than in winter. This is just opposite of the seasonal changes shown in Figure 1.