The American character‐figure CA as a measure of magnetic activity of the Earth

Abstract

A close relationship between radio‐transmission conditions and irregular fluctuations of the Earth's magnetic field has been recognized for some time. The nature of this relationship may be briefly stated as follows: At times when the variations of the Earth's magnetism are of a regular character transmission over long distances is generally good on all frequencies, but when the variations are irregular—that is, during magnetic “storms”—communication over high‐latitude paths is unsatisfactory or altogether impossible on the higher frequencies.In efforts to understand this relationship better, numerous investigators have made correlations of radio conditions and magnetic storminess. Various measures of storminess have been used—sometimes the daily range of magnetic change at a single station, sometimes a subjective estimate of storminess as assigned by the observer‐in‐charge of a magnetic station. Such measures are not fully adequate as they only partially represent the conditions at a single point on the Earth. Magnetic storms affect the entire Earth although local conditions may vary considerably.