NORTH SOUTH ASYMMETRY OF SC/SI MAGNETIC VARIATIONS OBSERVED ALONG THE210-DEGREES MAGNETIC MERIDIAN/

Magnetic field data from the 210 degrees magnetic meridian chain of st ations have been analyzed to examine which component of the DL and DP fields dominates main impulses of sc and si observed on the ground. Th e DL and DP fields correspond to transfer processes from the magnetopa use through the magnetosphere to the Earth's surface and through the p olar ionosphere into the equatorial ionosphere, respectively. Northern and Southern Hemisphere asymmetry of sc and si disturbances appears a t low and middle latitudes. Amplitude ranges of the sc and si main imp ulses observed at low-latitude conjugate pairs (L = 2.1 and 1.6) in th e summer hemisphere are about twice as wide as those in the winter hem isphere. The equatorial enhancement of sc and si main impulses can be seen at Yap island (Phi = -0.3 degrees) during the daytime at 0600-180 0 LT. These observational facts can be interpreted by invoking an asym metry in the Northern and Southern Hemisphere twin-vortex-type ionosph eric currents driven by the DP field, i.e., by invoking enhanced ionos pheric conductivities in the summer hemisphere. The instantaneous pene tration of sc and si-associated DP fields through the ionosphere from the polar region to the equator must play an important role in the ene rgy transfer of sc and si disturbances from the solar-wind region to t he magnetic equator.