On the Geomagnetic Storm on February 11, 1958
The great geomagnetic storm which occurred at 01 h 25 m UT Feb. 11, 1958, was analysed using the data of 28 station's hourly values during 3 days from -24 hr to +48 hr of the SC. And the equivalent current vectors of the DS field were compared with the world-wide patterns of the blackouts. From this study three remarkable characteristics deduced as follows.
(1). The most active DS field happened suddenly one hour after the SC (+1 hr) almost all over the auroral zone and the polar cap. This is an exceptional characteristic compared with the other IGY storms with sudden commencements, of which DS fields grew generally with the development of the Dst field.
(2). Polar cap blackouts began to occur 13 hours before the SC (-13hr). The horizontal component of the geomagnetic field, which had been almost calm until this time, began to decreased simultaneously. The pre-sc disturbance reached the maximum stage 6 hours before the SC (-6hr). At that time, observed H decreases reached 500 gammas approximately, at the auroral zone stations, College, Tiksy and Dixon.
The rotational trends of the distribution of the equivalent current vectors of the pre-sc disturbance at -11 hr and -1 hr were clockwise on the morning side and counterclockwise on the evening side. Then it was concluded that the current systems of the initial phase were equivalent to the intensified pre-sc current systems.
(3). The southward shift of the auroral zone was observed clearly associated with the development of Dst. In the developing stage of the Dst until the maximum at +9 hr, the southward shift of the auroral zone was observed in the European zone on the morning side, while in the recovering stage of the Dst since +9 hr the shift was observed in the zone from Alaska to Kamchatka with a distribution of spiral pattern. And the red homogeneous arc of aurora was observed at Memambetsu (φm=34.1) in Japan during the period from 19 h to 22 h LT.