POLAR-CAP FIELD RESPONSE TO IMF B-Y SECTOR CHANGES ON QUIET DAYS AT ALONGITUDE LINE OF OBSERVATORIES

The fields for quiet days of 1976 and 1977 are studied for a line of o bservatories established near 76 degrees E longitude in the Northern H emisphere, Using a special spherical harmonic analysis (SHA) technique to separate the external and internal parts of the observed field cha nges when the geomagnetic activity index Kp had low values, we demonst rate that a selection of SHA polynomials with (n - m) > 1 serves to is olate the polar region field contributions. The equivalent external cu rrent representation of the polar fields (sometimes called Sq(p)) show two vortices separated by the day-night hemisphere boundary. When plo tted in local time, the nighttime current patterns are usually observe d to change positions to earlier locations when the IMF sector structu re varied from the Toward (IMF B-y negative) to the Away (IMF B-y posi tive) direction (with respect to the Sun) of the arriving solar wind f ield at the magnetospheric boundary. The addition of these changing po lar current patterns with the more stable lower-latitude Sq (solar qui et-time) dynamo currents probably accounts for the previously reported sector effects in the Sq. The technique of selective separation of po lynomials shows that the Sq could be adequately described by the SHA p olynomial terms having (n - m) < 2 and that there persisted a small mi d-latitude vortex of SHA polynomial (n - m) = 1 currents in winter. Th e polar region activity and the Southern Hemisphere Sg vortex extensio n into the Northern Hemisphere had overshadowed the wintertime express ion of the low amplitude Sq vortex in the full-field daily variation r ecords.