Dependence of the polar cusp on the north-south component of the interplanetary magnetic field

Abstract

Ogo 5 observations of the polar cusp on November 1, 1968, show that the north-south component of the interplanetary field exhibits control over both the location of and the physical processes occurring in the polar cusp. When the interplanetary field turned from north to south, the polar cusp moved equatorward. During intervals when the interplanetary field was southward, the electron temperature in the polar cusp was lower and the currents were stronger than when the interplanetary field was northward. Also during these intervals of southward field, regions of apparently rapidly varying currents were encountered within the cusp. Associated with these regions were enhanced VLF electric field levels. When the interplanetary field was northward, quasi-monochromatic Pc 1 waves close to but below the proton gyrofrequency and energetic electrons (E > 50 kev) were observed. Most of these observations are consistent with the existence of merging of the interplanetary magnetic field with the dayside magnetospheric field when the interplanetary field is southward and the absence of merging when it is northward. The dependence of electron temperature on field direction remains unexplained.