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A study of the features of slowly varying and pulsating ionospheric absorption events recorded by the Kiruna riometer in the morning hours indicates that both events involve electron precipitation on the atmosphere. In addition, it is concluded that pulsations in absorption do not represent a separate type of event but, instead, arise from slowly varying events owing to modulation of electron precipitation by hydromagnetic processes.
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R. R. Brown (1964) studied this question.
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