The processes responsible for the effective longitudinal transport of solar energetic particles ( SEPs ) are still not completely understood .
We address this issue by simulating SEP electron propagation using a spatially 2D transport model that includes perpendicular diffusion .
By implementing , as far as possible , the most reasonable estimates of the transport ( diffusion ) coefficients , we compare our results , in a qualitative manner , to recent observations at energies of 55 – 105 keV , focusing on the longitudinal distribution of the peak intensity , the maximum anisotropy and the onset time .
By using transport coefficients which are derived from first principles , we limit the number of free parameters in the model to : ( i ) the probability of SEPs following diffusing magnetic field lines , quantified by a \in [ 0 , 1 ] , and ( ii ) the broadness of the Gaussian injection function .
It is found that the model solutions are extremely sensitive to the magnitude of the perpendicular diffusion coefficient and relatively insensitive to the form of the injection function as long as a reasonable value of a = 0.2 is used .
We illustrate the effects of perpendicular diffusion on the model solutions and discuss the viability of this process as a dominant mechanism by which SEPs are transported in longitude .
Lastly , we try to quantity the effectiveness of perpendicular diffusion as an interplay between the magnitude of the relevant diffusion coefficient and the SEP intensity gradient driving the diffusion process .
It follows that perpendicular diffusion is extremely effective early in a SEP event when large intensity gradients are present , while the effectiveness quickly decreases with time thereafter .