The equatorial latitude of auroral activity during 1972-1977

The equatorial latitude of auroral activity has been derived from both electron and optical observations with the DMSP satellites. Essentially all of these observations have been used to produce a nearly continuous plot of invariant geomagnetic latitude versus time during the 5-year interval June 1972 - September 1977. This plot has two main characteristics: (1) a diurnal variation of approximately ±5° which is somehow associated with the precession of the Earth's magnetic dipole axis about the Earth's rotation axis and (2) an irregular variation of roughly 5-10° for intervals of one to several days associated with the occurrences of solar flares and coronal holes. With the help of a condensed, Bartels-type display of these measurements, we conclude that (1) modest auroral expansions (to [lambda] ~ °) occur during the main body of high-speed streams from coronal holes and (2) great expansions (to [lambda] < 55°) occur at the leading edge of a high-speed stream or at a flat-produced interplanetary shock.