THE PROPAGATION OF SOLAR ENERGETIC PROTONS - COMPARATIVE-STUDIES IN 2CASES WITH MARKEDLY DIFFERENT SCATTERING CONDITIONS

In this work we analyze solar particle and interplanetary magnetic fie ld (IMF) data recorded during three solar particle events observed on board Helios I on 1978 April 11 and on 1980 June 7. The fluctuating co mponent of the IMF is markedly different in the three cases, the field being very turbulent in the first and very quiet in the second period comprising the other two events. Energetic particle intensities and a ngular distributions also show different characteristics. Particles pr opagate in a regime of strong scattering on 1978 April 11, while for 1 980 June 7 conditions of weak scattering dominate. Pitch angle scatter ing coefficients and mean free paths for energetic protons are determi ned by three different methods: (1) power spectra of IMF fluctuations following quasi-linear theory (QLT), (2) numerical simulations of test particle trajectories using IMF data, and (3) particle time intensity and time anisotropy profiles and angular distributions. Recent invest igations (Wanner and Wibberenz 1991b, 1993; Wanner et al. 1993a, b; Dr oge et al. 1991, 1993) have only compared QLT and particle observation s. In this work, we add to these the results of particle trajectory si mulations, which are obtained using assumptions different than the QLT calculations. Resulting mean free paths are very similar for the thre e different approaches, being about 0.015 AU for the event of 1978 Apr il 11 and about 1 AU for the events of 1980 June 7 at 100 MeV particle energy. The agreement found between the mean free path results from t he different approaches shows that QLT with the slab wave model leads to a level of scattering coincident with energetic particle determinat ions for some cases with widely differing scattering conditions. We al so find that the shapes of the pitch angle diffusion coefficients do n ot agree. A discussion of the implications of these findings on the of ten cited discrepancy between mean free paths determined via QLT and t hose found by analysis of particle time intensity and anisotropy profi les is given.