North/South Asymmetry of sc/si Magnetic Variations Observed along the 210.DEG. Magnetic Meridian.

Abstract

Magnetic field data from the 210° magnetic meridian chain of stations have been analyzed to examine which component of the DL and DP fields dominates main impulses of sc and si observed on the ground. The DL and DP fields correspond to transfer processes from the magnetopause through the magnetosphere to the Earth's surface and through the polar ionosphere into the equatorial ionosphere, respectively. Northern and Southern Hemisphere asymmetry of sc and si disturbances appears allow and middle latitudes. Amplitude ranges of the se and si main impulses observed at low-latitude conjugate pairs (L = 2.1 and 1.6) in the summer hemisphere are about twice as wide as those in the winter hemisphere. The equatorial enhancement of se and si main impulses can be seen at Yap island (Ψ =-0.3°) during the daytime at 0600-1800 LT. These observational facts can be interpreted by invoking an asymmetry in the Northern and Southern Hemisphere twin-vortex-type ionospheric currents driven by the DP field, i.e., by invoking enhanced ionospheric conductivities in the summer hemisphere. The instantaneous penetration of sc and si-associated DP fields through the ionosphere from the polar region to the equator must play an important role in the energy transfer of sc and si disturbances from the solar-wind region to the magnetic equator.