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Criteria for geomagnetic phenomenon classification (Kakioka)

The Kakioka Magnetic Observatory assigns Class A, B or C to typical geomagnetic phenomena for ssc (the rapid onset of a geomagnetic storm), si, bay, sfe, pc and pi (qualities representing the prominence or clarity of an event, as detailed below).

Classification was initiated from the IAGA Copenhagen Conference in 1957 in response to suggestions for Class A (= very distinct), B (= fair, ordinary, but unmistakable) and C (= doubtful). Class determination for ssc is based on geomagnetic storms occurring between July 1957 and December 1968.

ssc classification

ssc	A	B	C	Remarks
	15nT ≦ a	6nT ≦ a < 15nT	3nT ≦ a < 6nT	"a" represents ssc amplitude. The actual ssc class may be lower than this classification, which is determined from the amplitude of an abrupt onset and the rate of change, as well as the shape and activity of a magnetic storm (based on the disturbance range).

si classification

si	A	B	C	Remarks
	2 < α	1 ≦ α ≦ 2	α < 1	α is the ratio of the si amplitude (nT) to the maximum amplitude (nT) of other irregular changes within a three-hour period centered on this time (excluding geomagnetic short-period changes occurring during the period). The lower limit of B has a magnitude of 5 nT, and the rate of change is assumed as approximately 3 nT/min.

bay classification

bay		A	B	C
	Relatively calm periods	35nT or above	15nT or above	10nT or above
	Disturbance periods	Extremely prominent	40 - 50nT or above	25nT or above

sfe classification

sfe		A	B	C	K index
	Calm periods	20nT or above	7nT or above	2 - 3nT or above	0 - 2
		25nT or above	10nT or above	5nT or above	3 or above

pc classification

pc		A	B	C	Remarks
		1.8nT or above	1.8 - 0.7nT or above	0.7 - 0.4nT or above
	Disturbance periods	2.7nT or above	2.7 - 1.0nT or above	1.0 - 0.6nT or above	For pc waveforms disrupted by overlapping with other phenomena

pi classification

pi	/th>	A	B	C	Remarks
		3.9nT or above	3.9 - 2.0nT or above	2.0 - 0.7nT or above
	Disturbance periods	5.9nT or above	5.9 - 3.0nT or above	3.0 - 1.0nT or above	For pc waveforms disrupted by overlapping with other phenomena