Symposium on the Last Total Solar Eclipse of the Millennium in Turkey, İstanbul, Turkey, 13 - 15 August 1999, vol.205, pp.202-207
Intensity variation of cosmic rays and its dependence on various factors are important for understanding the interplanetary medium. Primary cosmic rays, observed in the interplanetary system, have galactic and extragalactic origins. Their intensity is known to vary inversely with the intensity of the solar wind. A solar effect on primary cosmic rays in the interplanetary space is implied by a solar modulation. The 11-year (more precisely, 22-year) variation, the diurnal variation, and the 27-day variation of secondary cosmic ray particles are well known types of solar modulations observed from the earth. Bhattacharyya et al. (1997) have observed a solar modulation of secondary cosmic ray particles during a total solar eclipse which may be considered as a different effect. During the total solar eclipse of 11 August 1999, the variation in the local secondary cosmic ray density in Istanbul has been investigated by means of gamma rays. The eclipse in Istanbul was 95%, not total, but this has been sufficient to verify the previous results. In our experiment, the mean drop in low energy cosmic ray flux of gamma rays has been detected as 11%. We propose that such observations may reveal the impact of ;local secondary cosmic rays on the climate.