EFFECTS OF THE INTENSE SOLAR-ACTIVITY OF MARCH JUNE 1991 OBSERVED IN THE OUTER HELIOSPHERE

The properties of the large-scale global merged interaction region (GMIR) generated by the intense solar events of March and June 1991 are studied using the available solar wind, interplanetary magnetic field, and energetic particle data from the observing network of pioneer 10 and Voyagers 1 and 2 in the outer heliosphere. At heliocentric distances extending to 55 AU the delayed effects of this enhanced solar activity are observed in the form of large increases in the solar wind velocity and interplanetary magnetic field and significant decreases in the galactic cosmic ray intensity. For low-energy ions (5-MeV protons) there was a single long-lived event extending over a period of some 6 months. Near the strongest interplanetary disturbances the H and He spectra are best represented by similar exponentials in momentum/nucleon (i.e., particle velocity at these energies). Over the rest of the event the characteristic momentum for He, (P0)H, is generally approximately 0.66 for hydrogen. These spectra and the consistently low H/He ratio (25.3) at 2 MeV/nucleon closely resemble that observed in corrotating interaction regions events. Despite the strong north/south asymmetry in the solar activity, the interplanetary disturbances produced the same net decrease in the galactic cosmic ray intensity of ions >70 MeV at the three widely separated spacecraft when the effects of the long-term recovery are taken into account. A comparison of the relative intensity of MeV ions at these three spacecraft suggest that the. most intense solar events occurred on the back side of the Sun in time periods adjacent to the March and June episodes of solar activity. It is argued that this GMIR as a system is responsible for the low-frequency radio emission observed by the Voyager Plasma Wave experiment some 1.46 years after the onset of the March 1991 activity.