11 Year variation in third harmonics of cosmic ray intensity on quiet days

Abstract

The aim of this work is to study the long term variation in third harmonics of cosmic ray intensity on sixty quietest days in a year using the data of high latitude and low latitude neutron monitoring stations during the solar cycle 20-22. It has been observed that in spite of the abrupt change in the amplitude and phase of third harmonic of cosmic ray intensity, the amplitude of third harmonics is relatively larger during the solar cycle 21 as it is observed during the declining phase of earlier solar cycle 20.Therefore this enhancement explicit point out 11 year periodicity in third harmonics of cosmic ray intensity at equatorial neutron monitoring stations. Further, the phase shift to later hours during the year 1990 showing the dependence on the polarity of solar magnetic field, which is attributed to drift effect at high latitude neutron monitoring station