Jökull - 01.12.1962, Page 58

Fig. 1. Type C, A and R oscillations observed in Reykjavik on Feb. 1—2 1963. The record
begins at 2100 h and ends at 1200 h. Typical A oscillations occur around miclnight whereas
typical C oscillations commence in the early morning. Very faint R oscillations are observed at
the end of the irregular oscillations around midnight. The short period oscillations at the bot-
tom of the record are either A or R oscillations.
GENERAL PATTERN OF THE
OBSERVED OSClLLATfONS
A train of similar magnetic oscillations, con-
tinuous or interrupted, will in the following
be regarded as a single magnetic event. The
main criteria for similarity are the form and
the period of the oscillations. On this basis an
event may last for a considerable part of the
day.
As shown by Benioff (1960) the magnetic
events can be divicled into rather distinct
groups. fn the case of the present observational
material from California a grouping into 4
groups, A, C, DP and DI, and R, appears
suitable.
(A) Short-periocl oscillations. Infrequent
long beating trains of sinusoidal or quasi-sin-
usoidal oscillations with periods 0.5 to 2.5 sec
observed in California preferably cluring the
night or in the early morning. A typical ex-
antple is shown in Fig. 1.
(C) Medium-period oscillations. Frequent
trains of sinusoidal or quasi-sinusoidal oscilla-
tions with periods 10 to 40 sec observed prefer-
ably during the day. An example is shown in
Fig. 1.
(DP) and (DI) Pulses and irregular trains.
Transients in the form of regular pulses with
relatively long periods and long irregular trains,
both observed in California preferably during
the night. An example of a DP event is shown
in Fig. 2.
(R) Short-period rider oscillations. Infre-
quent trains of sinusoidal or quasi-sinusoidal
oscillations with periods 0.5 to 3.0 sec accom-
panying some of the C, DP and DI oscilla-
tions. Some of the small short-period oscilla-
tions shown in Fig. 1 may represent R events.
The groups are here designatecl according to
56 JÖKULL