MULTI-SPACECRAFT OBSERVATIONS OF PARTICLE EVENTS AND INTERPLANETARY SHOCKS DURING NOVEMBER DECEMBER 1982

We present a sample of solar energetic particle events observed betwee n November 18 and December 31, 1982 by the HELIOS 1, the VENERA 13, an d IMP 8 spacecraft. During the entire time period all three spacecraft were magnetically connected to the western hemisphere of the Sun with varying radial and angular distances from the flares. Eleven proton e vents, all of them associated with interplanetary shocks, were observe d by the three spacecraft. These events are visible in the low-energy (about 4 MeV) as well as the high-energy (30 MeV) protons. In the larg est events protons were observed up to energies of about 100 MeV. The shocks were rather fast and in some cases extended to more than 90-deg rees east of the flare site. Assuming a symmetrical configuration, thi s would correspond to a total angular extent of some interplanetary sh ocks of about 180-degrees. In addition, due to the use of three spacec raft at different locations we find some indication for the shape of t he shock front: the shocks are fastest close to the flare normal and a re slower at the eastern flank. For particle acceleration we find that close to the flare normal the shock is most effective in accelerating energetic particles. This efficiency decreases for observers connecte d to the eastern flank of the shock. In this case, the efficiency of s hock acceleration for high-energy protons decreases faster than for lo w-energy protons. Observation of the time-intensity profiles combined with variations of the anisotropy and of the steepness of the proton s pectrum allows one in general to define two components of an event whi ch we term 'solar' and 'interplanetary'. We attempt to describe the re sults in terms of a radially variable efficiency of shock acceleration . Under the assumption that the shock is responsible not only for the interplanetary, but also for the solar component, we find evidence for a very efficient particle acceleration while the shock is still close to the Sun, e.g., in the corona. In addition, we discuss this series of strong flares and interplanetary shocks as a possible source for th e formation of a superevent.