| Summary: | Observations using HF radiometers, a sensitive riometer, and near vertical-incidence Doppler sounding on three widely spaced frequencies, were made to determine
the kind and frequency of occurrence of overhead ionospheric perturbations, at sub-auroral latitudes (L = 3.5), associated with magnetic variations, during the sunspot minimum period (1963-1966). It was found that F layer and sporadic E. layer (electron) ionisation density (and possibly collision frequency and velocity) perturbations, but not except during ''storms" energetic particle precipitation, are associated with all types of magnetic rapid variations. The maximum association is for 'Pt' micropulsations, the minimum for daytime magnetic
bays.
Statistics on the percentage of events of various kinds observed and on the percentage of hours when related events occurred are presented.
The nature of the various associations is discussed in terms of the currently published theories of micropulsations and ionospheric perturbation. It is concluded that available theories require further elaboration before the experimental results can be interpreted
to specify unique processes for the various kinds of events.
A new kind of event appearing to involve modulation
of electro jet currents by E region waves of 90 seconds period was observed.
Magnetic events without Doppler perturbations were observed indicating that observed associations are not merely direct magnetic perturbation of the magnetoionic refractive index but rather require electron distribution perturbations. === Science, Faculty of === Earth, Ocean and Atmospheric Sciences, Department of === Graduate
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