The response of the quiet-time auroral configuration to short- and long-term interplanetary magnetic field variations

Abstract

Observations from the IMP-8 satellite of the interplanetary magnetic field (IMF) are compared with areas of the polar region bounded by the aurora as observed by the Viking spacecraft during quiet-time conditions (IMF B_z northward). A variety of energy-coupling functions are investigated and it is determined that the auroral distribution can be best described by the inclusion of azimuthal terms in addition to standard energy-coupling functions. The auroral distributions for B_z northward support antiparallel merging as a mechanism whereby energy is transferred to the magnetosphere from the solar wind. As well, however, when the polar angle is small the region bounded by the auroras expands and may be controlled more by wave interaction at the magnetopause. Observations by the Viking spacecraft indicate a dominance of dusk sector polar arcs in the spring time and dawn sector arcs in the fall (post equinox). Two alternative mechanisms can explain the observations. One involves the ordering of the IMF in a solar equatorial coordinate system while the other involves the Sun's polarity and the traversal of the Earth's orbit through different heliographic latitudes. A test is proposed whereby the two hypotheses can be investigated during the next solar cycle.