Jökull - 01.12.1962, Page 67

Table 15 in order to illustrate a possible cor-
relation between the period and the magni-
tude.
TABLE 15
Number of A events observed in California
grouped with regard to period and magnitude.
Magnitude
I + II III + IV
Peröcl range (a) + (b) 29 8
(c) + (d) 32 11
The data given in the Tables 10 to 15 indi-
cate the following relations:
(1) The A oscillations occur definitely on
days of lower than average Ap figure, that is,
on days o£ low magnetic activity.
(2) On the other hand, the average Ap for
the larger magnitude of the A events is slightly
higher than for the smaller magnitudes. How-
ever, the difference is so small that it may be
insignificant.
(3) The longer periods are associated with
slightly lower Ap figures than the shorter
periods.
(4) Period and magnitude appear uncorre-
lated.
There is no obvious correlation between the
A oscillations and the events observed on slow-
run magnetograms. However, the following ob-
servations may be mentioned.
There are 80 A events in the interval Nov-
ember 1, 1954 to February 28, 1957 occurring
on 69 days and within an interval of 10 hours
of the day.
On the slow-run magnetograms from Tucson,
Arizona, there are on the same days ancl hours
a total of 216 events that may be classified as
the commencements of magnetic bays.
A total of 14 A events commence approxi-
mately simultaneously with the commencements
of the bays. Moreover, 14 additional A events
appear to have some relation with magnetic
bays. A relevant fact is that magnetic bays have
a similar preference for days of low magnetic
activity as the A oscillations.
At this juncture it is difficult to evaluate the
significance of the above observation. Further
data are needecl.
There may also be a slight tendency of the
A oscillations to occur 5 to 10 days after a
magnetically disturbecl period.
An attempt was made to correlate A oscilla-
tions with ionospheric data. Only very incom-
plete results were obtained. The A oscillations
appear'to occur preferably simultaneously with
tlie minimum of the fcF2, that is, the minimum
of the spatial maximum electron concentration
in the F2 layer of the ionosphere.
SUMMARY OF MAIN DATA
ON TYPE A OSCILLATIONS
OBSERVED IN CALIFORNIA
(1) Field amplitude: Up to 0.3 microgauss.
Magnitude scale based on tlie maximum
amplitude of north-south component of
the magnetic field.
(2) Period: 0.5 to 2.5 sec. Period band of in-
dividual events relatively stable and nar-
row.
(3) Character: Sinusoidal oscillations witli fair-
ly regular beating of a period 50 to 100
sec.
(4) Period-magnitude relation: No correlation.
(5) Diurnal pattern: Occur during the night
or in the very early morning. Duration
1/2 to 5 hours.
(6) Annual pattern: Frequency of occurrence
higher in the summer. Commence at an
earlier hour o£ the day in the summer.
Period may possibly be shorter in the
summer.
(7) Relation of distant recording stations: No
differences observed.
(8) Relation to events on slow-run magneto-
grams: Occur on days of a relatively low
Ap figure. Larger magnitudes associated
with slightly larger Ap averages. Longer
periods associated with lower Ap averages.
In cases the A events appear to coincide
with magnetic bays on the Tucson slow-
run magnetograms. The A events may pos-
sibly have a tendency to occur 5 to 10 days
after a magnetically disturbed period.
(9) Relation to solar cycle: Frequency of oc-
curence decreases greatly with the increas-
ing solar activity.
(10) Relation to ionosphere conditions: Occur
preferably at the time of lowest f0F2.
(11) Relation to C, DP and DI oscillations: No
relation.
JÖKULL 65