Cosmic Ray Sidereal Diurnal Variation of Galactic Origin Observed by Neutron Monitors

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 (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, 1961-1969 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 stationyears 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 between two hemispheres were analyzed. The results were interpreted on a theoretical basis of the three-dimensional anisotropy and its annual modulation model (Nagashima and Ueno, 1971; Nagashima et al., 1972a, b) that the former (difference) can be identified with the spurious sidereal diurnal 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 monitor 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-Castagnoliet al.'s finding is not real, but virtual even for the deep underground observations (rigidity region _500 GV) due to modulation with the spurious sidereal diurnal variation of solar origin, based on the threedimensional anisotropy and its annual modulation. In the present analysis, we examine the dependence of the sidereal variations on Sun's polar https://ntrs.nasa.gov/search.jsp?R=19850026687 2017-09-12T19:24:34+00:00Z