Study of tri‐diurnal variation of galactic cosmic radiation

Author:
  • SASant P. Agrawal
    Sant P. Agrawal
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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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