A New Approach to Interplanetary Transport of Solar Energetic Particles in Impulsive Events

Impulsive,³He-rich events originate close to the interface between slow solar wind overlying active regions and a faster solar wind coming from small coronal holes. This causes large-scale magnetic compressions to be an interplanetary environment for solar energetic particle (SEP) transport in impulsive events, which is typically ignored by SEP modelers. We have modeled SEP transport in a simplified corotating solar wind structure to estimate the possible effect of the rising wind speed on particle anisotropy and spectra at 1 AU. Along with traditional modeling of SEP transport in the static magnetic field and the field-aligned solar wind flow of the corotating frame of reference, we have formulated and tested a new model that is the first model of focused transport applicable to a general case of SEP propagation in realistic, dynamic, and structured solar wind. Numerical modeling shows that a fast increase of the wind speed by only 200 km s⁻¹ can strongly affect the SEP flux anisotropy at 1 AU. Accurate analysis of impulsive SEP events can be done with the use of solar wind data, SEP flux anisotropy measurements, and the new approach that accounts for the solar wind structures associated with the sources of impulsive events and uses the general solution of the focused transport problem applicable to SEPs in realistic solar wind.