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AP Index

Published by NOAA National Centers for Environmental Information | National Oceanic and Atmospheric Administration, Department of Commerce | Catalog Last Checked: April 12, 2026 at 04:40 AM | Dataset Last Updated: September 18, 2015 at 12:00 AM
Planetary Amplitude index - Bartels 1951. The a-index ranges from 0 to 400 and represents a K-value converted to a linear scale in gammas (nanoTeslas)--a scale that measures equivalent disturbance am- plitude of a station at which K=9 has a lower limit of 400 gammas.

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