The rigidity dependence of solar particle scattering mean free paths

The rigidity dependence of solar particle scattering mean free paths in the range from 0.1 to a few GV is a key parameter to distinguish between different models for the nature of wave-particle interactions and of interplanetary magnetic turbulence. Here we present an analysis of electron and ion data, covering a large portion of the above range, obtained from modeling intensity and anisotropy profiles of a series of solar particle events in 1982 August that show exceptionally large but finite mean free paths. Combined with particle measurements from previously analyzed events that exhibit mean free paths in the range of 0.02 to 0.5 AU, we find that a uniform shape of the functional form of the rigidity dependence, which varies only in absolute height for different events, can explain all observations. These results place severe constraints on any propagation theory and rule out a number of recently suggested models to improve the standard quasilinear theory of particle scattering. Our findings may indicate that the component of the turbulence the particles interact with does not vary much with respect to its decomposition into different modes and their respective spectral and angular wavenumber dependencies, and basically the total power of this component is responsible for the level of the mean free paths.