ON REPRODUCTION OF LONG-TERM COSMIC-RAY MODULATION AS SEEN BY NEUTRONMONITOR STATIONS

The dependence of cosmic-ray intensity on 21st solar cycle phenomena h as been studied using monthly cosmic-ray values from nine world wide N eutron Monitoring Stations. For this purpose the long-term cosmic-ray modulation is modelled by treating the most appropriate source functio ns among various solar, interplanetary and terrestrial activity indice s as the input and the cosmic-ray intensity as the output of a linear system taking into account the corresponding time-lag. In this way the modulated galactic cosmic-ray intensity has been reproduced to a cert ain degree as the cosmic-ray variations follow the observations with a standard deviation of similar to 10%. Still remaining short-term vari ations in all stations with periods of 2.7 and 3.7 months can possibly be related to the galactic origin of cosmic-rays. The Simpson solar w ind model improved by the spherically symmetric diffusion-convection t heory can describe our proposed method.