Study of tri‐diurnal variation of galactic cosmic radiation

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.

Solar cycle variations of cosmic ray intensity and large-scale structure of the heliosphere

“…However, the method of power spectral analysis has provided an easy way to extract the small periodic signals in the presence of noise (Lanzerotti et aI., 1981). Such an analysis has confirmed the existence of second (12-hr period) and third harmonics (8-hr period) of daily variation (see Agrawal, 1981, and references therein). The theoretical study of Owens (1981) relating to the third harmonic should be mentioned.…”

Interplanetary Transients and Cosmic-Ray Anisotropy

“…The average amplitudes of diurnal and semi-diurnal anisotropies are found to be larger than normal during the initial phase of the stream but smaller than normal during the decreasing phase of the stream, and the phase is observed to remain almost constant (Agrawal, 1981). This suggests that the diurnal as well as semi-diurnal variation of galactic cosmicray intensity may be influenced by the solar polar coronal holes.…”

Characteristics of Enhanced and Low Amplitude Anisotropic Wave Trains and Interplanetary Transients

“…The average amplitude of diurnal and semi-diurnal anisotropy are found to be larger than normal during the initial phase of the stream while it is smaller as compared to the normal during the decreasing phase of the stream and phase is observed to remain almost constant (Agrawal, 1981), which infer that the diurnal as well as semi-diurnal variation of GCR intensity may be influenced by the solar polar coronal holes. The changes have also been observed in the amplitude and phase during the HSSWS coming from coronal holes (Munakata et al, 1987;Iucci et al, 1981).…”