Propagation of flare protons in the solar atmosphere

Abstract

The velocity dispersion for a large number of solar proton events is analyzed in the energy regime of 10–60 MeV. It is found for all events that the time from the flare to particle maximum t _m is well represented by a sum of two components. The first component which is energy independent describes the propagation in the solar atmosphere, the second component describes the propagation in the interplanetary medium giving a velocity dispersion v × t _m = const. The additional study of time intensity profiles, onset times, and multispaceprobe observations reveals that the propagation in the solar atmosphere consists of three processes: (1) A rapid transport process in the initial (≲ 1 h) phase after the event fills up a “fast propagation region (FPR)”, which may extend up to ≈ 60° from the flare site and which is tentatively identified with a large unipolar magnetic cell as seen on Hα synoptic charts, (2) a large-scale drift process which is energy independent with drift velocities v _D in the range 1° ⩽ v _D ⩽ 4°h^-1, and simultaneously (3) a diffusion process which yields the general broadening of the intensity time profiles for eastern hemisphere events, which is, however, of less importance than previously assumed.