Features of global geomagnetic Sq field from 1980 to 1990 -: art. no. 1252

[1] Seasonal and year-to-year variations of geomagnetic Sq field were examined using the global equivalent current system for one solar cycle from 1980 to 1990. It was confirmed that the Sq current intensity is about half in solar minimum of that in solar maximum and its year-to-year variation is relatively smooth for each month. At 0200 UT, vortices in the winter and summer hemispheres shift to the afternoon and morning side, respectively, but with phase delay by about 1 or 2 months. On the contrary, at 1400 UT the northern vortex is located in the morning side of the southern vortex in most months of all years, and seasonal variation of the location is not so clear. As for the morphology of the current system, it was found that there are only two types in the shape of the Sq current system at 0200 UT. That is, it shows northern summer type from April to September and northern winter type from October to March, and there is no equinox type, and it clearly differs in March from that in September. This feature is similar to that of the seasonal variation type of the tidal winds in the upper mesosphere.