Propagation of Pc 1 micropulsations from high to low latitudes

It is shown, for typical profiles of ionospheric parameters, that a duct exists in the F region of the ionosphere in which hydromagnetic waves are efficiently guided. The duct has a low-frequency cutoff at about 0.5 cps, showing that the observed variation of emission frequency with latitude is largely a propagation effect. Duct attenuation is small during the night hours, when the majority of Pc 1 events are observed at middle and low latitudes, but it is large during the day. The calculated duct group velocity is of the same order as that given in initial reports of experimental observations.