Observed sidereal variations are corrected for the influence of spurious variation by a method using the antisidereal diurnal variations produced from the same 2nd order anisotropy (Nagashima, et al., 1983). It is demonstrated that the corrected variations are a resultant product of two constituents of galactic origin: one is north-south (N-S) symmetric and the other is N-S asymmetric

Fujii, Z.

Mori, S.

Nagashima, K.

Ueno, H.

Yasue, S.

English

NASA Technical Reports Server

3 5 SH 4. 4-3
Sidereal Anisotropies in the Median Rigidity Range
60-600GV in 1978-1983
H.Ueno, Z.Fujii, S.Mori*, S.Yasue* and K.Nagashima
Cosmic Ray Res. Lab., Nagoya Univ., Nagoya 464, Japan
*Depart. of Physics, Shinshu Univ., Matsumoto 390, Japan
i. Introduction
A great many observation has been made of the sidereal time variations
of cosmic rays with various detectors in a wide range of rigidities from
neutron monitors(effective primary rigidity 101°V), surface and under-
ground muon telescopes to small air shower arrays(1013 _ I014V), and
much data have been accumlated to explore the nature of the galactic
anisotropy, such as its origin and its propagation inside and outside
the heliomagnetosphere.
In low rigidity region, the observed sidereal diurnal variations con-
tain not only those of galactic origin but also those of solar and atmo-
spheric origin. The variations of the latter origin are called the
spurious sidereal variations, and almost all of them can be eliminated
by taking the difference between the variations observed by two component
telescopes pointing different directions (cf. Elliot and Dolbear, 1950).
This elimination method, however, cannot be applied to the variation
arising from the seasonal variation of solar anisotropy. A typical
example for this can be seen in the spurious sidereal diurnal variation
arising from the solar anisotropy of the 2nd order responsible for the
solar semi-diurnal variation(Nagashima and Ueno, 1971).
In the present paper, the observed sidereal variations are corrected
for the influence of this spurious variation by a method using the anti-
sidereal diurnal variations produced from the same 2nd order anisotropy
(Nagashima et al., 1983). It is demonstrated that the corrected varia-
tions are a resultant product of two constituents of galactic origin:
one is north-south(N-S) symmetric and the other is N-S asymmetric.
2. Data Analysis and Discussions
In the present analysis, we use the data from surface(NA__goya) and
underground(Misato and S_akashita) muon telescopes. Hereafter we abbre-
viate these stations to NAMS by picking up the top letter of the name
of the stations. These data cover the rigidity range of 60 to 600GV,
and the present work is concerned with 6-year averages of these data in
the period of 1978-1983.
In Table i, 6-year averages of the observed sidereal diurnal varia-
tions of NAMS are listed, together with those of the anti-sidereal
diurnal variations and are shown in Fig.l and Fig.2. Also listed in
the table are some characteristics of the telescopes(Fujimoto et al.,
1984). Errors of the amplitudes are derived from the dispersion of
. yearly vectors.
The spurious sidereal diurnal variations are produced by various
noises such as the atmospheric effects and also transient cosmic ray
intensity variations. In the present analysis, these noises can be
eliminated statistically by taking 6-year averages and also by intro-
ducing the unknown vector common to all directional components at each
station in the best fit calculation. The spurious sidereal diurnal
variation is also produced from cosmic ray flow perpendicular to the
solar equatorial plane. This variation is sector-structure dependent
and is called Swinson-type(cf. Swinson, 1969). This variation could
https://ntrs.nasa.gov/search.jsp?R=19850026688 2020-03-20T16:45:54+00:00Z
36 SH 4. 4-3
Table i 6-year averages of observed sidereal diurnal variations of NAMS for
1978-1983, together with those of associated anti-sldereal diurnal
variations and also corrected varlat_ons for Nagashlma's component
(see text). Some characteristics of the telescopes are also shown.
Errors of the amplitudes are derived from the dispersion of yearly
vectors.
Zenith & CeoErsphic Hedlsn CountinE Amplitude(%)'& Phsee(hr)of Harm*nice of'
Azimuth Direction RIgldlty Rate 6 Years AveraEee 1978-1983
STATION TELESCOPE Z A A # PNE(GV) xlO4/hr Anti-Sidereal let Sidereal 18t Corrected Sidereel let
NAGOYA V 0 ° - 35"H 137 ° 60 276.0 .0342.008 20.8 .0112.008 16.1 .0212.0U 4.4
Omse N 30* 0 e 65"N " 66 125.0 .0372.008 19.5 .0182.007 14.5 .0182.010 3.3
E ,, 90 °.. 30*N 172" 67 120.0 .0262.008 19.7 .0022.008 3.8 .0262.009 3.2
S - 180 ° 5"N 137" 64 123,O .0142.009 21.3 .0092.008 4.2 .0222.Oll 4.3
W " 270* 30°N 102 ° 63 126,0 .0352.007 22.3 .0162.007 18.7 .0182.011 5.0
HISA_O V 0* 36"N 138" 145 28.0 .0322.007 21.9 .028_.O07 19.0 .0122.008 0.9
34we N 33* 39" $7eH 177 &' 155 10,7 .0332.007 " 19.5 .030±.007 "15.8 .0072.009 21.9
E " 129" 120N 164" 143 14,2 .012±.007 21.7 .018±.008 21.9 .O182.008 0.3
S " 219" 90N 117" 155 10,7 .0252.005 23.6 .0192_O07 23.9 .022_.O08 4.6
W " 309 ° 510E 95 ° 156 9.8 .O372.006 23.3 .0252.006 19.5 .0122.007 5.1
SAKASHITA V O* 36"N 138 ° 331 39.0 .O32i.004 23.0 ,017±.004 22.9 .028±,004 4,2
801we N 41" 346 ° 730N 104 ° 401 6.2 .0232.004 22.6 .0082.004 17.6 .0152.005 6.4
E ,, 76 ° 35"N 188 ° 384 '7.6 ,O21_.004 21.2 .0212.004 22.6 .0292.003 1.5
8 " 166" 5°S 147" 387 6.7 .0182.004 1.3 .054_.004 2.6 .056_.005 3.8
W " 256* 180N 96" 444 5.6 .019i.004 2.2 .040±.OO3 3.8 .O432.OO4 9.4
HN 60 ° 346 e 77"H 26; 595 2.4 .0022.004 6.4 .002i,004 15.2 .0042.006 13.5
SS " 166" 23"51 151* 540 2.7 .015_.OO5 8.1 .086±.005 2.6 .072_.006 2.4
oh 0h
,6h NAG.
18h0_ §
h
h
Hsh
.... 6h MIS. _s
_ h lab • ' ' , , Sh MIS.
SS_ 005%
[
18h_ : - ..... 6h SAK. teha5..:0.05%
,2. f._jss
12h *
Fig. l 6-year averages of observed side-
real diurnal variations of NAMS Fig. 2 6-year averages of observed anti-
telescopes at Nagoya (NAG), sidereal diurnal variations of
Misato (MIS) and Sakashita (SAK) NAMS telescopes for 1978-1983.
for 1978-1983.
3 7 SH 4. 4-3
be canceled by taking averages of the all period due to almost equal
appearance of the toward and away sectors.
Spurious sidereal diurnal variation is also produced by a systematic
annual variation of the solar diurnal variation arising from a solar
diurnal variation caused by a stationary anisotropy responsible for the
solar semi-diurnal variation(Nagashima and Ueno, 1971). According to
the recent study(Nagashima et al., 1983), the spurious variation can be
eliminatedby multiplying the observed anti-sidereal diurnal variation
by 0.947, rotating the vector counterclockwise by 68 °, and subtracting
it from the observed sidereal diurnal vector.
The corrected sidereal diurnal variations of NAMS are also listed in
Table 1 and are shown in Fig.3. As is seen in the figure, the corrected
sidereal diurnal variations at Sakashita station are statistically sig-
nificant, while the variations at Misato and Nagoya stations are com-
parable with the corresponding dispersion errors. As the counting
rates at Misato and Nagoya are large, the large errors are supposed to
be caused by the scattering of year-to-year vectors mainly due to the
insufficient correction for transient solar diurnal variations. On the
other hand, the relative configuration of the vectors of each station
seems to be reasonable from the standpoint of geometrical setting of
the component telescopes. This implies that real errors may be smaller
than the dispersion errors, and in this respect it is worthwhile exam-
ining the rigidity dependence of the corrected sidereal diurnal varia-
tions including those of the two stations.
oh Oh
' S
18h .... 6h NAG. 18h*'_-_-_- 6h
1!h 0.05% I. t2h
N S
18h ' ' :6 h MIS. 18_ : 6h
O,O5% l( h "
,h Oh
• - - - 3h SAK.//(t_"'_- _i" 6:": : : -: h
.,_. _JN 0.05% "-1--
" 12' 12h
Obs. Cal.
Fig.3 6-year averages of corrected Fig.4 Best fit case of corrected sidereal
sidereal diurnal variations of diurnal variations of NAMS tele-
NAMS telescopes for 1978-1983. scopes for 1978-1983. The cross
marks are the common vector for
each stacion calculated by the
least squares method.
3 8 SH 4. 4-3
In order to derive the anisotropy, we assume the following in the
best fit method as
l) two terms of N-S symmetric and N-S asymmetric types are assumed in
the anisotropy for a better fitness between the observed and the
expected variations,
2) from the observed fact that the amplitudes are larger for the deeper
underground stations, we reasonably assume the low cutoff rigidity
PL in the flat rigidity spectrum, and
3) the unknown vectors are introduced to eliminate the spurious noises
as mentioned above.
Tentative results using coupling coefficients given by Fujimoto et al.
(1984) are obtained;
N-S symmetric term (P_-type)
the amplitude 0.079+0.007%, the phase 3.5hr and PL=200GV
N-S asymmetric term (P_-type)
the amplitude 0.035+0.007%, the phase 14.9hr and PL=200GV
In the present calculation, SS-component at Sakashita station is not
included because of larger risidual error probably due to some helio-
spheric effect which occurs in sidereal semi-diurnal variations (Fujii
et al., 1984). The calculated variations in the best fit case are
shown in Fig.4.
3. Summary
i. The correction for the spurious sidereal variation using the anti-
sidereal variation is indispensable to the study of sidereal anisot-
ropy in low rigidity region.
2. Galactic sidereal anisotropy can be explained better with two terms
of N-S symmetric and N-S asymmetric types than the usual uni-direc-
tional anisotropy only.
References
Elliot,H. and Dolbear,D.W.N. (1950) Proc. Phys. Soc. A, 63, 137.
Fujii,Z. et al. (1984) Proc. Int. Symp. CR Mod. Morioka, 364.
Fujimoto,K. et al. (1984) Rep. CR Res. Lab., Nagoya Univ., No.9.
Nagashima,K. and Ueno,H. (1971) Rep. Ionos. Space Res. Japan, 25, 212.
Nagashima,K. et al. (1983) Nuovo Cimento, 6C, 550.
Swinson,D.B. (1969) J. Geophys. Res., 74, 5591.
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Sidereal anisotropies in the median rigidity range 60-600GV in 1978-1983

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