| Abstract | Using the experimental data of the high counting rate neutron and meson monitors, the solar tri-diurnal anisotropy of galactic cosmic radiation has been investigated for the period 1962–79. The enhancement of the average tri-diurnal amplitude observed by all the detectors during 1973–75 provides sufficient signal to noise ratio to obtain its variational characteristics. The observations are consistent with an interplanetary anisotropy having a power law rigidity spectrum exponent ≈ 1. The tri-diurnal amplitude varies as cos³ λ, where λ is the effective asymptotic latitude of the detector. The annual average tri-diurnal amplitude shows a significant positive correlation with the semi-diurnal amplitude for the period 1968–79. The correlation, however, is poor for the earlier period 1962–67, which may be due to the presence of significant modulation of semi-diurnal anisotropy with periods of 22-year sunspot magnetic cycle. An analysis using groups of days with high and low solar wind speed shows greater amplitude of both the tri-diurnal and semi-diurnal waves for the group of days with high wind speed. This result coupled with the observation of a factor of 2 increase in both amplitudes during 1973–75, a period when high speed solar wind streams were prevalent, suggests that solar polar coronal holes may influence both the solar tri-diurnal and semi-diurnal variation of galactic cosmic ray intensity. |
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