Study of cosmic ray intensity variation during quiet interplanetary periods

Abstract

Various solar controlled disturbances in interplanetary medium represented by solar flares, coronal holes, solar wind streams, generally produced significant decreases in cosmic ray intensity as well as enhancement in geomagnetic field. The continuous occurrence of low values of the geomagnetic field disturbance index Ap is known to be a good indicator of undisturbed conditions prevailing in the interplanetary medium. Selecting such events of continuous days of low Ap values (Ap ≤ 6, for atleast 5 days), we have analysed daily values of the cosmic ray intensity for a number of events for the intervals, before during and after the events, for the period 1976 to 86. The results show that the cosmic ray intensity is maximum during event period. As expected, the associated interplanetary medium features V, B, Bz and also show minimum fluctuation during the event periods. Hormonic analysis for the representative years 1977, 1981 and 1986, provides conclusive evidence of observing relatively smaller amplitudes of the diurnal variation during quiet periods.