OBSERVATIONS OF GALACTIC COSMIC-RAY MODULATION DURING EARTH-DIRECTED CORONAL MASS EJECTIONS

We describe three cosmic-ray decreases observed by the energetic parti cle telescope ERNE on board SOHO spacecraft during the period January - May, 1997. The decreases in cosmic-ray proton intensities in the ene rgy range above 50 MeV were observed after the passage of interplaneta ry shocks on February 9, April 10, and May 15. All the shocks were pro duced by Earth-directed coronal mass ejections. The amplitudes of the decreases compared to the counting rates just before the shock arrival were 8.5 %, 14 %, and 7 %, respectively. The observed recovery times were 1, 4.2, and 5 days, respectively. After the February and May even ts the pre-shock levels were reached, but in the April event the recov ery was only to 3 % below this level. In each case, there were also cl ear indications of the passage of the ejecta. The energy dependences o f the cosmic-ray helium flux decreases at 12-100 MeV/n were similar to each other in the April and May events, while in the February event t he decrease was less pronounced.