Jökull - 01.12.1962, Blaðsíða 65

The majority of the DP oscillations appears
to coincide with sudden commencements and
magnetic bays recorded on the slow-run mag-
netograms from Tucson, Arizona.
The DI oscillations are characterized by an
irregular character and a longer duration than
the DP oscillations. No period can be defined.
The relation between the magnitude of DI
events and the Ap figure is given in Table 8.
Table 8 reveals a clear positive correlation
between the magnitude of DI events and the
Ap figure.
A great number of the DI events may coin-
cide with sudden changes of the field recorded
on slow-run magnetograms. However, the rela-
tion is obscured by the circumstances that the
DI events occur preferably on disturbed days
where the slow-run magnetograms are quite
irregular.
No results were obtained as to a correlation
of the DP and DI events with ionospheric
conditions.
OBSERVATIONAL DATA
ON TYPE A OSCILLATIONS
In the case of A oscillations it is found more
suitable to apply the computed maximum am-
plitude of the observed field component as the
basis for the magnitude scale. The A oscilla-
tions are generally of a very regular sinusoidal
character and the computation of the fielcl
amplitude is, therefore, quite accurate.
The magnitude scale applied is based on the
sensitivity of the Palomar recorder and is as
follows:
TABLE 9
Magnitude scale for A oscillations.
Maximum amplitude of the Magni
north-south field component tude
0.010 — 0.023 microgauss i
0.024-0.053 n
0.054-0.122 iii
0.123-0.280 IV
A list of all reliable observations of A oscil-
lations observed in California during the period
November 1, 1954 to February 28, 1957 is given
in Table 17 where the time of occurrence, re-
cord amplitude, period range and the comput-
ed magnitude are listed. The list comprises
80 events which occur on 69 days. The data
are plotted in Fig. 11 and 12.
Most of the A oscillations exhibit a pro-
nounced beating with periods 50 to 100 sec.
Tlie number of A events and the average
period during the interval between equinoxes
is given in the following Table 10.
The period of A oscillations may have a ten-
clency to be shorter during the summer than
during the winter. The relation is, however,
somewhat obscure and further data are needed
before conclusions can be drawn.
The total number of observed A events is
comparetively small. Therefore, in correlating
the magnitude and period to the Ap figure
only the total recording period frorn November
1, 1954 to February 28, 1957 will be considered.
Tlie relation between the magnitude and the
Ap figure is illustrated in Table 11.
Due to the fact that the magnitude groups
TABLE 10
Number of A event.s observecl in California and the average period
during intervals between equinoxes.
Interval
November 1. 54 to March 21. 55 . ..
March 22. 55 to September 21. 55 .
September 22. 55 to March 21. 56 .
March 22. 56 to September 21. 56 .
September 22. 56 to February 28. 57
Sum 80 Average 1.25
Number Average pe
15 1.15 sec
35 1.30
11 1.55
17 1.10
2 1.15
JÖKULL 63