Daily Ap Geomagnetic Index

The daily average Ap index from the Fredericksburg (mid-latitude) and Anchorage (high-latitude) stations, which monitor the Earth's magnetic field.

The Ap index ranges from 0 (very quiet) to 400 (extremely disturbed). An Ap index of 30 or greater indicates local geomagnetic storm conditions.

The a index, from which the Ap index is derived, is an "equivalent amplitude" index of local geomagnetic activity; "a" is related to the 3-hourly K index.