Abstract
Of the many suspected relationships between observable terrestrial phenomena and solar activity, as marked by sunspots, those longest recognized are the variations in the characteristics of the Earth's magnetic field and the occurrences of auroras. The advent of radio communication in recent years has opened up a new field for the investigation of conditions of ionization in the Earth's upper atmosphere and affords a new source of observational data for the study of solar‐terrestrial relationships. The simultaneous occurrence of radio fade‐outs, solar eruptions, and violent changes in the Earth's magnetic field have received wide attention. The more general changes in radio transmission with the occurrences of auroras, and geomagnetic fluctuations accompanying increased sunspottedness are of a more gradual nature and probably follow in a somewhat different category from phenomena of the eruptive fade‐out.

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