Jökull - 01.12.1962, Qupperneq 59

Fig. 2. Type DP, C and R oscillations observed in Reykjavik on Dec. 9—10 1962. The record be-
gins at 1200 h and ends at 1200. A large DP event occurs at miclnight whereas typical C
oscillations occur also in the record.
Benioff (1960) who gives a more detailed de-
scription. However, Benioff’s group B is not
significant in the present material and his
group D has here been split up into DP and
DI events. Moreover, the rider oscillations, also
clescribed by Benioff, have here been treated
as a separate group.
A great number of authors, especially Euro-
pean investigators, have grouped the micro-
pulsations into two main groups, that is, con-
tinuous pulsations, Pc, and transient pulsations,
Pt. This is less specific than Beniofi’s grouping.
It is clear that the type C ancl D events fall
into the P(. respectively the Pt groups.
There is a considerable literature on magne-
tic micropulsations ancl the effort devoted to
the study of this phenomenon has been increas-
ing at a fast rate mainly during the past decade.
Tlie work of the Japanese group (see Kato and
IVatanabe, 1957), Jakobs (see Westphal and
Jakobs, 1962), Campbell (see Campbell and
Matsushita, 1962) and Troitskaya (1961) shoukl
be mentioned.
METFIOD OF CLASSIFICATION
The observational material will in the follow-
ing be treatecl in accordance with the above
grouping of the magnetic events. For each event
the following data have been extracted from
the records:
(1) The time of commencement ancl end of
each event.
(2) 'I'lie main period, or periods, where a
period can be defined.
(3) The maximum amplitude.
Generally, there are no difficulties in obtain-
ing approximate data on the commencement,
the end and the periods of the events, except
in the cases of the DI oscillations where a period
can not be defined.
JÖKULL 57