The ionosphere over Halley Bay

The ionospheric phenomena observed at Halley Bay are briefly described and the influence of the Weddell Sea magnetic dip anomaly stressed. Some ionization is generated in the lower ionosphere by solar photo-ionization processes at solar zenith angles up to about 100°. The F 2 layer variations appear to be dominated by movements of ionization which can also be seen near the maximum of the F 1 layer. Ionization drift velocities in the E region reverse with season and are greater in winter than in summer. Other features of drift and absorption are generally consistent with those expected. The incidence of spread F is very anomalous, being essentially a quiet-day phenomenon. High, cusp and one type of flat Es also predominate when magnetic conditions are quiet. The relations between auroral and retardation Es , a type of flat Es , polar blackout and magnetic activity are discussed more fully. The station appears to be exceptionally well placed for the study of ionospheric phenomena.