External Sq currents in the India-Siberia region

Abstract

The Sq current systems for quiet days of 1976 and 1977 were studied for observatories established near 76° E. longitude in the northern hemisphere. We used a special spherical harmonic analysis technique to separate the internal and external contributions of the quiet field variations and to determine the equivalent external current contours responsible for the Sq field variations on the sixth and twenty-first of each month. The average ratio of the external to internal spectral power was 6.7 in 1976 and 7.4 in 1977. Focus positions for the India-Siberia region external Sq current vortex, near 22° to 29°, were found to be at lower geomagnetic latitudes than for Europe and North America. The usual mid-latitude vortex current, reaching 11.0 to 13.2 × 10⁴ A in summertime, disappeared completely during winter months in both the years. The Sq current position was affected clearly by the off-spin axis position of the north geomagnetic pole. Throughout the 2 years, we also found small current vorticies near 70° to 80° geomagnetic latitude, which we ascribed to auroral region activity on quiet days.