Modulation of galactic cosmic ray anisotropy in heliomagnetosphere: Seasonal variation of sidereal daily variation     

K. Nagashima  I. Morishita  S. Yasue 《Planetary and Space Science》1983,31(11):1259-1268

In the previous paper (Nagashima et al., 1982), we have reported the yearly averaged modulation of galactic cosmic ray anisotropy in the heliomagnetosphere. In the present paper, we analyze the seasonal (annual) dependence of the modulation, using the frequency modulation method. The seasonal variation of the sidereal daily variation produced from the anisotropy is resolved into variations with proper sideband frequencies, such as solar and anti-sidereal variations. These side-band variations are predominant in the rigidity region of 10² ～' 10³ GV and show the following characteristics.(1) Being similar to the average sidereal variation, they are strongly dependent on the polarity state (‘positive’ or ‘negative’) of the heliomagnetosphere.(2) The side-band variations with frequencies lower than the sidereal frequency (366 cycle/year) generally predominate over those with higher frequencies. The most predominant variations are produced from the component of the uni-directional anisotropy projected to the Earth's rotation axis and could be observed as the solar and anti-sidereal diurnal variations.(3) If the flat neutral sheet of the heliomagnetosphere is replaced with the wavy neutral sheet, side-band variations in the positive state tend to diminish with the increase of the heliolatitudinal extent of the wavy neutral sheet, while those in the negative state almost retain their magnitude.(4) These variations depend also on the observation periods when the Earth is located either in the “toward” field or in the “away” field. This T-A dependence changes with the transition from the positive state to the negative and increases with the increase of the heliolatitudinal extent of the wavy neutral sheet. The most remarkable T-A dependence is observed in solar diurnal variation arising from the component of the unidirectional anisotropy projected to the Earth's rotation axis and can be used for the determination of the direction of the anisotropy.  相似文献   

Twenty-two year modulation of cosmic rays associated with polarity reversal of polar magnetic field of the sun     

K. Nagashima  I. Morishita 《Planetary and Space Science》1980,28(2):195-205

The existence of the 22-year modulation of cosmic ray intensity is pointed out, using data of the ion chamber at Huancayo and the neutron monitors at Ottawa and Deep River for about four solar cycles. The modulation consists of two discrete states (high and low intensities), corresponding respectively to those of the polarity of the polar magnetic field of the Sun. This can be interpreted on the basis of the following hypothesis; when the polar magnetic field of the Sun is nearly parallel to the galactic magnetic field, they could easily connect with each other, so that galactic cosmic rays could intrude more easily into the heliomagnetosphere along the magnetic line of force, as compared with those in the anti-parallel state of the magnetic fields. The observed intensity difference between two states is about 4.3 ± 0.2% for neutron monitor (P_c = 1.5GV). The abnormal increase in proton (0.28–0.42 GV) and electron (0.41-3.24 GV) fluxes in the 20th solar cycle and the sudden appearance of anomalous components (He⁺, etc.) since 1972 can be also explained on the basis of the present hypothesis. The transition between the two states has a time lag behind the polarity reversal, depending on the cosmic ray rigidity, such as about 1 year for the neutron monitor (P_c = 1.5 GV) and about 3.5 years for low rigidity components (P < 1 GV). These time lags could be explained on the basis of the generalized Simpson's coasting solar wind model and the general diffusion-convection theory on some assumptions.  相似文献