Jökull - 01.12.1962, Side 60

On the other hand, the maximum amplitude
is a figure of a more doubtful significance.
Generally, C and A oscillations exhibit a pro-
nounced beating and the maximum amplitude
is in many cases a very transitory characteristic.
Therefore, it appears more appropriate to apply
the maximum amplitude only for a classifica-
tion of the magnitude of the events on the
basis of a relatively coarse scale. A 4-step scale
will be introduced in the following.
This scale can [>e basecl on thc observed
maximum amplitude of the north-south com-
ponent of dH/dt, or on the computecl maxi-
mum amplitude of the north-south component
H. The former procedure will be appliecl in
the case of C, DP and DI oscillations whereas
the latter will be applied in the case of A oscil-
lations.
The main observational clata in the case of
the various types of events are given in Fig. 3
to 12. The numerical data on the magnitude
scales are given below.
METHOD OF ANALYSIS
In analysing the observed data the following
items appear to be of main interest:
(1) Diurnal pattern.
(2) Annual pattern.
(3) Period-magnitude relation.
(4) Correlation with events recordecl on slow-
run magnetograms.
(5) Correlation of records from distant sta-
tions.
(6) Correlation with solar activity.
(7) Correlation with ionospheric conditions.
(8) Correlation with cosmic-radiation inten-
sity, auroras, whistlers and other natural
electromechanical phenomena.
Items (1) to (3) can be obtained directly from
the recordecl data ancl do at this juncture not
require further discussion.
A measure of the average daily activity of
the earth’s magnetic field is given by the average
planetary amplitude A which is computed for
each day by the magnetic observatory in De
Bilt, Holland.
In the following the magnitude and the
period of the various observecl events will be
correlatecl with the Ap figure of the day on
which they occur. The correlation pattern is
obtained by comparing the average Ap figures
of days associated with the various magnitudes
and period ranges.
Moreover, an attempt will be made to corre-
late the individual events with events observecl
on slow-run magnetograms. For this purpose
the magnetograms from the observatory in
Tucson, Arizona, were applied.
The largest distance between any two of the
4 stations in Southern California is between
Haiwee and Palomar, or about 250 km. Tliis
distance is relatively small. The degree of iden-
tity of the records from these stations has been
studied.
The solar activity during the periocl from
November 1954 to February 1957 is characteriz-
ed by a sharp rise in the sunspot activity from
a minimum to a fairly high level. The general
pattern of the variations in the frequency of
the various magnetic events during this change
can be obtained directly from the records.
The main observational data on the condi-
tion of the various layers of the ionosphere are
the critical frequency f0 and the apparent height
h of the layers. These data are now furnished
by a great number of stations. A fairly com-
plete stucly of the relation between the magne-
tic events and the conditions in the ionosphere
requires a considerable work and has not been
carriecl out. The only step carried out is an
attempt at correlating a few individual magne-
tic events with ionospheric data given Iry the
Stanford Station in Palo Alto, California. This
station is located some 500 km north of the
recording stations in Southern California.
A study of the relations of the magnetic
events to the phenomena listed in item (8)
could not be made. Special facilities would be
required for this purpose.
OBSERVATIONAL DATA
ON TYPE C OSCILLATIONS
The magnitude scale for C oscillations is
based directly on the maximum amplitude of
the records, that is on the maximum amplitude
of the north-south component of dFI/dt. The
4-step scale has been selected as follows:
58 JÖKULL