Results of ionosphere measurements utilizing transmissions at vertical incidence and made weekly over a period of 18 months are discussed. Typical graphs of diurnal variations of the E-layer critical frequency and its relation to the ionizing for ce of the s un are shown for three seasons. Similar graphs for the F2layer are included a s well as a seasonal curve of midday , and maximum critical frequencies of this layer. The absence of midday F 2 critical frequencies during the summer is pronounced.
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