| Term: | ap index |
| Definition: |
A mean, 3-hourly ”equivalent amplitude” of magnetic activity based on K index data from a planetary network of 11 Northern and 2 Southern Hemisphere magnetic observatories between the geomagnetic latitudes of 46° and 6° by the lnstitut fur Geophysik at Gottingen, Germany; ap values are given in units of 2 nT. |