A-index

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The A-index provides a daily average level for geomagnetic activity, based on the K-index. Because of the non-linear relationship of the K-scale to magnetometer fluctuations, it is not meaningful to take averages of a set of K indices. Instead, each K is converted into a linear scale called the "equivalent three hourly range" a-index (note the lower case). The daily A index is the average of eight "a" indices.

Both A and K-index reports are available on WWV or WWW.

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