Daily variation of cosmic rays during quiet and disturbed periods in 1965 and 1966
Data from super neutron monitors at Deep River, Churchill, Resolute, and Alert have been used to study the daily variation of cosmic-ray intensity during 1965 and 1966. Intensities have been examined on a daily, weekly, and monthly basis as a function of the asymptotic direction of vertically incident 7.5-BeV particles. The data have been analyzed in an earth-centered solar-ecliptic coordinate system in which daily (due to the earth's rotation) and seasonal (due to the inclination of the earth's axis to the ecliptic plane) variations of the asymptotic directions are considered.During undisturbed periods the daily variation has been examined by applying a digital filter to the pressure-corrected data and also to the data after subtraction of a variable-amplitude Parker–Axford theoretical diurnal variation. Particular attention has been paid to the dependence of the observed daily variation on the solar-ecliptic latitude of the asymptotic direction.Seventy-three percent of the weeks considered in 1965 and 1966 give the phase of the first harmonic in a direction 85° ± 35 °E. Sixty percent of the weekly periods show a daily variation as a function of solar-ecliptic latitude which is in agreement with the Parker–Axford "streaming-velocity" theory. During Forbush decreases the diurnal phase shifts towards earlier hours and the amplitude increases to two to three times the predecrease level.