The equatorial latitude of auroral activity during 1972–1977

Abstract

The equatorial latitude of auroral activity has been derived from both electron and optical observations with the DMSP satellites. Virtually all of the observations that were obtained during the 5-year interval June 1972-September 1977 have been used to construct a nearly continuous plot of invariant geomagnetic latitude versus time.

This plot has two main characteristics: (1) A diurnal variation of approximately ± 5° which is associated with the precession of the Earth's magnetic dipole axis about the Earth's rotation axis; (2) an irregular variation of roughly 5–10° for intervals of one to several days associated with the occurrence of solar flares and coronal holes.

With the help of a condensed, Bartels-type display of these measurements, we conclude that: (a) Modest auroral expansions (to Λ ~ 60°) occur during the main body of high-speed streams from coronal holes; (b) great expansions (to Λ < 55°) occur only during intervals of intense interplanetary magnetic fields such as may occur at the leading edge of a high-speed stream or at a flare-produced interplanetary shock.