AstroLAB's Interesting Tables
Classifcation of geomagnetic disturbances
Description	K index	A index
Quit	0 - 2	< 8
Unsettled	3	8 - 15
Active	4	16 - 29
Minor Storm	5	30 - 49
Major Storm	6	50 - 99
Severe Storm	7 - 9	100 - 400
Source: The Cambrdige Encyclopedia of the Sun (Kenneth R. Lang)
A index: a daily index of local geomagnetic activity; the average of the eight 3-hourly
a indices.
K index: a 3-hourly, quasi logarithmic local index of geomagnetic activity ranging from
0 to 9; the 3-hourly local a index of geomagnetic activity ranges from 0 to 400.