Latitudinal and longitudinal variation of Pc 4, 5 pulsations and implications regarding source mechanisms

Early theoretical studies of geomagnetic pulsations dealt with the oscillation of individual magnetic lines of force in the toroidal mode. In recent years it has become increasingly clear that the pulsations are organized in the azimuthal direction so that treatment of an oscillating surface of the field lines may need to be considered rather than oscillations of individual field lines. In this paper evidence for the azimuthal dependence of Pc 4, 5 pulsation characteristics will be presented. In addition, the latitudinal characteristics of the ground perturbation pattern and the local time variation of these pulsations will be discussed in the context of some of the source mechanisms proposed for long period micropulsation activity.