Daily definitive Ap index

Three-hourly sub-auroral geomagnetic activity indicator provided by GFZ Potsdam, Germany. Contributing observatories provide definitive K values to GFZ, that are standardized to Ks and used to compute Kp as a mean. The ap index is then obtained as a linear scale representation of Kp according to a mapping table. The Ap index is the daily mean of the eight values of 3-hourly ap indices.