The am annual-diurnal variations 1959-1988 : A 30-year evaluation

This paper is devoted to a reevaluation of the annual and universal time variations of the geomagnetic activity through a study of the am index over a 30-year period starting in 1959, taking into account the interplanetary magnetic field polarity. A visualization of the annual diurnal variations, showing the continuous evolution of the times of the diurnal maximum and minimum, is applied both to this extended data set and to the simulation of the main processes invoked to explain these variations. The various contributions of the different processes to the annual-diurnal variations of the activity are discussed, including the Russell-McPherron and the McIntosh effects, as well as a third source introduced in this study. One concludes that three contributions, two of which being attached to the Bz southward influence, must be combined to account for the observations.