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Tabulations of hourly values of the ionospheric parameters for 18 northern-hemisphere stations have been used to derive diurnal variations in the occurrence of “blackout” conditions. Contour plots are presented showing the diurnal average percentage of time during which blackout conditions prevailed, the amplitude of the diurnal variation, and the time of maximum frequency of occurrence. Changes in the contours with season and with magnetic activity are discussed.
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Vaughn Agy (1954) studied this question.
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