Cosmic ray sidereal diurnal variations observed by neutron monitors are analyzed for the period 1961 to 1978, by adding 134 station years data to the previous paper (Nagashima, et al., 1983). Also the dependence of the sidereal variations on Sun's polar magnetic field polarity is examined for two periods; the period of negative polarity in the northern region, 1961 to 1969 and the period of positive polarity, 1970 to 1978. It is obtained that for the former period, the amplitude A=0.0203 + or 0.0020% and the phase phi=6.1 + or - 0.4 h LST and for the latter period, 0.0020% and phi=8.6 + or - 4 h LST, respectively

Ishida, Y.

Mori, S.

Morishita, I.

Nagashima, K.

English

NASA Technical Reports Server

31
SH 4.4-2
COSMIC RAY SIDEREAL DIURNAL VARIATION OF GALACTIC
ORIGIN OBSERVED BY NEUTRON MONITORS
Y. Ishida, K. Nagashima*, S. Mori** and I. Morishita***
Department of Physlcs, Fukushima University, Fukushima 960-12, Japan
*Cosmic-ray Research Lab., Nagoya University, Nagoya 464, Japan
**Department of Physics, Shinshu University, Matsumoto 390, Japan
***Gifu College of Dentistry, Hozumi-cho, Gifu 501-02, Japan
ABSTRACT
Cosmic ray sidereal diurnal variations observed by
neutron monitors are analyzed for the period 1961-1978, by
adding 1D4 station-years data to the previous paper (Naga-
shima et al., 1983). Also the dependence of the sidereal
variations on Sun's polar magnetic field polarity is exam-
ined for two periods; the period of negative polarity in
the northern region, 1961-1969 and the period of positive
polarity, 1970-1978. It is obtained that for the former
period, the amplitude A=0.0203±0.0020% and the phase
_=6.1_0.4 h LST and for the latter period, _9 _007±
0.0020% and @=8.6±0.4 h LST, respectively.
1.Introduction
In the previous paper (Nagashima et al., 1983; hereafter referred to
as Paper I), we presented the analyzed results of the cosmic ray sidereal
diurnal variations observed by neutron monitors, by using 620 station-
years data from a worldwide net_k for th_ period 1958-1979. It was
shown that the sidereal variations averaged over the above period for the
Northern Hemisphere are significantly different from the corresponding
variations in the Southern Hemisphere. Both difference and average be-
tween two hemispheres were analyzed. The results were interpreted on a
theoretical basis of the three-dimensional anisotropy and its annual mod-
ulation model (Nagashima and Ueno, 1971; Nagashima et al., 1972a, b) that
the former (difference) can be identified with the spurious sidereal di-
urnal variation arising from annual modulation of 2nd order anisotropy in
space responsible for the solar semi-diurnal variation. And the latter
could be regarded as being due to uni-directional galactic anisotropy
(see detail, Paper I). In the present work,we analyze the neutron mon-
itor data by adding 134 station-years tothe previous ones, in the same
manner as in Paper I for the period 1961-1978.
9ini-Castagnoli et al. (1975) pointed out the association of the
sidereal diurnal variations at deep underground stations in the northern
. hemisphere with changing Sun's polar magnetic field polarity. For the
period of negative polarity in the northern region, the observed sidereal
vectors were around 20 h LST, while for the period of positive polarity,
the vectors were observed at _3 h LST. Very recemtly, Nagashima et al.
(1984) pursued this problem in detail, and demonstrated that Cini-Castag-
noliet al.'s finding is not real, but virtual even for the deep under-
ground observations (rigidity region _500 GV) due to modulation with the
spurious sidereal diurnal variation of solar origin, based on the three-
dimensional anisotropy and its annual modulation. In the present analy-
sis, we examine the dependence of the sidereal variations on Sun's polar
https://ntrs.nasa.gov/search.jsp?R=19850026687 2020-03-20T16:45:52+00:00Z
32
SH 4.4-2
magnetic field polarity for two periods; for the negative period in the
northern region (1961-1969) and for the positive period (1970-1978).
2.Analysis
The data used in the present analysis are those of neutron monitors
from a worldwide network for the period 1961-1978. The total amount of
data in the Northern and Southern Hemispheres are respectively 544 and
142 station-years by adding 134 station-years to them. The added data
are mostly concentrated on 1974 to 1977.
The analysis is made in the same manner
as in Paper I. The top panel of Fig. i show
oh
the first harmonies of the observed daily
J-_- 6 variations for Northen (N) and Southern (S)
"'_ _8-_ _ "8 Hemispheres and are; or the (N), the ampli-
i_ tude A=0.0123+_0.0019% and the phase ¢=9.0+0.3
0h - h LST and for the (S), A=0.0286+0.0037% and
¢=6.7+0.4 h IST, respectively.
_'_ i,-_ 6 Fig. i shows their difference first har-
_ monics (N-S)/2 and average (N+S)/2 for two
Hemispheres; for (N-S)/2, A=0.0099+0.0014%
and ¢--17.3+_0.5h LST and for (N+S)/2
_a___[6o A=0.0196+0.0014% and ¢=7.4+0.3 h LST, respec-(N+s)/_ tively. For comparision, the corresponding
I " expected variations are shown for flat rigid-12
ity spectrum with an upper cut-off rigidity
of 300 GV. The present results reconfirm the
The firstharonicof previous results and support the conclusion
observed sidereal daily var- in Paper I.
iations for the Northern (N)
and Southern(S) Hemispheres, In order to examine the dependence of
together with theirdiffer- the sidereal diurnal variation on Sun's polar
ence (N-8)/2 and theiraver- magnetic field polarity in neutron monitor
age (N+S)/2 with solidmarks, rigidity region, we separate the variations
The corresponding expected
variationsare alsoshown into two groups according to Sun's polar
with openmarks, field polarity; the negative period showing
toward field polarity in the northern region
(1961-1969) and the positive period showing away field polarity (1970-
1978). The number of data used and their average cut-off rigidities are
tabulated in Table 1. These are not necessarily balanced for both hemi-
spheres, but we regard them almost conjugate with respect to the north-
south. The sidereal diurnal variations of all the station-years for N
Table 1 Number of data and average cut-off rigidity.
m
Negative period Positive period
(1961-1969) (1970-1978)
Station-years Cut-off (GV) Station-years Cut-off (GV)
_orthern
_emlsphere 253 2.86 291 3.66
Southern
Hemisphere 78 4.07 6_ 3.68
33
SH 4.4-2
and S for two periods are
.0_ Oh
,.g.ti_.i_ T°.L_" io.,_, shown in Fig. 2. In the
(i_z-19@) _ " ' I figure, the distributions
•..[. •
• '" .'}'i'/. ".'' ' _ ferent from those of S for
i.'_., both periods
I:" _''''" " Fig. 3 shows the mean
i" vectors for N and S for
these two periods, NI and
'" $1 for the negative period
_2. _2_ (1961-1969) and N2 and $2
for the positive period
o_ o_ (19701978)Po,ltl,.perioa .o.,_. o.,_. - , respectively.
(z97o-_978_ The numerical values ; their
averages and each disper-
" .'i.....:' s _ .. sions are tabulated in Ta-
• ,':i " : .[ - .. ble 2. In the vectors with
• . -. ,,,..,, .. a notation (N+S)/2 ex-
• "" ;":_.',:" ' '":" .":': presses the variation com-
. .' .,..-.": ,
:..-.:;::, mon to both hemispheres ofi
north-south symmetric type.
This could be regarded as
,2, ,2. being due to uni-direction-
al galactic anisotropy as
has been discussed in
Sidereal diurnal variations of all the Paper I, and is shown Fig.
statlon-years for N and S for two periods; 4. It is obtained that for
negative (1961-1969)and positive (1970-1978) the negative period, the
perlods.
oh oh
n: negati,te period
o O:neg_tive period p: positive period
• e:pomltiTeperiod
3.01% 0.01%
NI $1
m , @------_-6 m_- ' ®_-6
® ®,
12 12
Averaged sidereal diurnal
.variations for N and S for two _ Sidereal diurnal variations
periods; oowith figure i for (N+S)/2 for two periods; negative
negative period (1961-1969)and _ (n) and positive (p) period.
e ewith figure 2 for positive
. period (1970-1978).
Negative period Positive period
* (1961-1969 ) (1970-1978 )
. Table 2 Observed sidereal
Amp.(%)xlO -_ Phase(h) Amp.(%)xlO -_ Phase(h) diurnal variations for N
znd S for t_o periods.
N 94 (16) 6.0 (0.6) 182 (19) 10.3 (0._) Also (N+S)/2 is shown.
Figures in the parentheses
S 312 (36) 6.2 (0._) 261 (36) 7._ (0.5) express the dispersions.
(_+s)/_ _03 (20) 6.1 (o._) 2o7 (20) 8.6 (0._)
S4
SH 4.4-2
amplitude A=0.0203+0.0020% and the phase ¢=6.1+0.4 h LST and for the
positive period, A=0.0207+0.0020% and @=8.6+0.4 h LST. It is noteworthy
that the present averages are exceptionally significant from the statis-
tical point of view.
3.Discussion and Conclusion
The present results of the sidereal diurnal variation, (N+S)/2, com-
mon to both hemispheres are statistically significant for two periods;
the negative (1961-1969) and the positive (1970-1978) period of Sun's
polar magnetic field as shown in Fig. 4. In these variations, the spuri-
ous sidereal variations may be eliminated by taking a long-term average.
And also the spurious sidereal diurnal variation caused by annual modula-
tion of the solar diurnal variation produced from a stationary anisotropy
responsible for the solar semi-diurnal variation (Nagashima, 1984), can
be eliminated due to its north-south asymmetric nature.
Also as shown in Fig. 4, the sidereal diurnal variations for these
two periods are significantly different from each other (several times
larger than the dispersion error). On the other hand, a recent work of
Nagashima et al. (1984) demonstrated that the sidereal diurnal varia-
tions observed at deep underground stations in both hemispheres almost
coincide with each other, after correcting for the annual modulation ef-
fect of the solar diurnal variation for the negative and positive period
mentioned above. And they showed that these resultant variations are
stationary throught the periods 1958-1983, regardless of Sun's polar
magnetic field polarity reversal. The present result rosy somewhat con-
tradict their conclusion, which may be due to rather larger errors in
underground data.
As far as these two periods and the neutron energy regions are con-
cerned, a clear phase difference between two periods ; negative and posi-
tive periods, was obtained. A further analysis is necessary to derive a
definite conclusion.
4.Acknowledgements
The authors wish to express their sincere appreciation to all the
directors of the observation stations for providing invaluable neutron
monitor data. These data are obtained through WDC-C2. A large part of
the present calculations were made of Computer Center Fukushima Univer-
sity.
Referen ces
Cini-Castagnoli, G., Marocchi, D., H. Elliot, R.G. Marsden and T. Thamb-
yahpillai, Proc. lhth Int. Cosmic Rays Conf. (Munich). 4, 1453 (1975).
Nagashima, K. and H. Ueno, Rep. lonosph. Space Res., Japan, 25, 212
(1971) •
Nagashima, K., H. Ueno, K. Fujimoto, Z. Fujii and I. Kondo, Rep. lonosph.
Space Res., Japan, 26, 1 (1972a).
Nagashima, K., H. Ueno, K. Fujim_to, Z. Fujii and I. Kondo, Ibid., 2__6,
31 (1972b) •
Nagashima, K., S. Sakakibara, A.G. Fenton and J.E. Humble, Planet. Space
Sci., (in press, 1984).
Nagashima, K., Proc. Int. Symp. Cosmic Ray Modulation Heliosph. (Morio-
ka), 309 (198_).


Cosmic ray sidereal diurnal variation of galactic origin observed by neutron monitors

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