อภิธานศัพท์ฟิสิกส์ (อวกาศ)

A 3-hourly "equivalent amplitude" index of local geomagnetic activity; "a" is related to the 3-hourly K INDEX according to the following scale: K 0 1 2 3 4 5 6 7 8 9 a 0 3 7 15 27 48 80 140 240 400