Energetic Storm Particle Events Research Articles

Solar cosmic ray phenomena

This review attempts to present an integrated view of the several types of solar cosmic ray phenomena. The relevant large and small scale properties of the interplanetary medium are first surveyed, and their use in the development of a quantitative understanding of the cosmic ray propagation processes summarised. Solar cosmic ray events, in general, are classified into two phenomenological categories: (a) prompt events, and (b) delayed events. The properties of both classes of events are summarised. The properties considered are the frequency of occurrence, dependence on parent flare position, the time profile, energy spectra, anisotropies, particle species, velocity dispersions, etc. A single model is presented to explain the various species of delayed event. Thus the halo and core events, energetic storm particle events, EDP events and proton recurrent regions are suggested to be essentially of common origin. The association of flare particle events with electromagnetic phenomena, including optical, X-ray and microwave emissions is summarised. The conditions in a sunspot group, and solar flare that are considered to be conducive to cosmic ray acceleration processes are discussed. Considerable discussion is devoted to physical processes occurring near the Sun. Near Sun particle storage, and diffusion, and secondary injection processes that are triggered by a far distant solar flare are reviewed. In order to explain the considerable differences between aspects of the prompt and delayed events, we propose selective diffusion processes that only occur at early times in a solar flare. The type IV radio emissions at metric wave-lengths are suggested to yield direct evidence for the storage processes that are necessary to explain the properties of the delayed events, and also as yielding direct evidence of secondary injection processes. We conclude by briefly summarising the ionospheric effects of the solar cosmic radiation.

Corotating Forbush Decreases

A natural introduction to this topic is a brief discussion of two phenomena observable in interplanetary space near Earth—the energetic storm particle event (ESPE), and the recurrent Forbush decrease.

Cosmic-ray propagation processes: 2. The energetic storm-particle event

Seven examples of the observation of intense fluxes of ≈10-Mev charged particles associated with disturbances in the interplanetary medium during 1966 are discussed, and detailed data from four of them are presented. It is shown that there is an approximately one-to-one correspondence between such events and the onset of Forbush decreases initiated by solar flares. The particle fluxes exhibit characteristic time profiles, with a typical time scale of 6 hours. The particle fluxes are strongly anisotropic, and the direction of the anisotropy shows drastic temporal variations during the onset of the Forbush decrease. The fluxes of particles of energy ≈10 Mev are frequently considerably greater, while the energy spectra are usually noticeably softer than those observed during the preceding flare effect. A bidirectional anisotropy is commonly observed following the decreasing intensity phase of a Forbush decrease, the two directions of maximum flux being aligned parallel and antiparallel to the interplanetary magnetic field vector. It is shown that the energetic storm particles do not suffer any significant trapping in the magnetic regime associated with the onset of the Forbush decrease. It is shown that the various facts are consistent with the Parker ‘blast wave’ model for the interplanetary magnetic field associated with the Forbush decrease, while the Gold ‘magnetic bottle’ model is unable to explain the observed temporal variations in the anisotropic character of the particle fluxes. Studies of the net particle flux moving radially away from the sun suggest that the energetic storm particles are suffering acceleration within the magnetic field (i.e. within the shock front) associated with the onset of the Forbush decrease. It is suggested that the recurrent low-energy cosmic-ray events observed by other workers might consist of energetic storm particles associated with recurrent Forbush decrease events.