The importance of the maximum plasma frequency of the ionosphere in controlling the occurrence of blackout

For locations normally equatorward of the auroral oval, it is established that there is a strong inverse association between the variations in the maximum plasma frequency of the ionosphere and the occurrence of blackout. It follows from this that blackout is a poor indicator of enhanced ionospheric absorption for this zone. It is shown that the occurrence of blackout can be predicted reliably in solar minimum years for a particular location, using a combination of riometer and ionosonde data.

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