On the threshold effect of proton acceleraton in solar flares

Solar Cosmic Rays

“…Evidently, serious modeling efforts are required to reconcile different approaches to the problem and to eliminate obvious controversies in interpretation of recent observational data. In the whole, the problem of SCR spectrum formation remains unresolved: if in the range of low or moderate energies the spectrum and composition are determined by intimate local plasma processes (e.g., Miroshnichenko 1987Miroshnichenko , 1995Vlahos 1989;) deeply inside the solar atmosphere, the spectrum formation in relativistic range is very likely to govern by large-scale, extended magnetic structures high in the corona (Perez-Peraza et al 1992;Chertok 1995;Miroshnichenko , 2001Miroshnichenko et al 1996Miroshnichenko et al , 2000.…”

“…The main problems of fundamental interest in the theory of particle acceleration at the Sun lie now at two boundary domains of SCR spectra, namely, in low-energy (non-relativistic) and high-energy (relativistic) ranges. The most important of them are: initial acceleration from the thermal background (e.g., Vlahos 1989;Vlahos et al 1989;Miroshnichenko 1995;, and final stage of acceleration to extremely high energies of E p ! 100 GeV (e.g., Podgorny and Podgorny 1990;Miroshnichenko 1994Miroshnichenko , 1996Miroshnichenko , 2001Karpov et al 1998 and references therein).…”

“…Just the first phase of acceleration from thermal distribution is well-known to be the most interesting since it provides a preliminary energization (injection) and determines essentially a charge composition of accelerated particles. This phase proceeds on the local level when only kinetic "micro-processes" in the solar plasma are important (e.g., Miroshnichenko 1995;). On the other hand, in order to be accelerated to relativistic energies, suprathermal particles need quite different spatial scales, at least comparable to their gyroradii in the coronal magnetic fields.…”

“…This value was derived from data on magnetic field variations in solar active regions before major flares. A few evaluations of E at coronal heights differ by several orders of magnitude -from~3 Â 10 À2 to >10 2 V cm À1 (Miroshnichenko 1987(Miroshnichenko , 1990(Miroshnichenko , 1995Berezinsky et al 1990;Litvinenko and Somov 1995;Litvinenko 1996a;Somov 1992Somov , 2012. These values are large enough to accelerate the runaway electrons from thermal to sub-relativistic energies (~100 keV) in fractions of a second (Vlahos et al 1989).…”

“…The clear differences between the slopes of size distributions for proton, electron and electromagnetic flare emissions were shown to be very important (e.g., Miroshnichenko 1995) when interpreting an initial stage of acceleration of solar cosmic rays. More recently, in the light of a new arising paradigm of particle acceleration in different sources at/near the Sun (e.g., Reames 1995aReames , b, c, 1996Reames , 1999, we started an extended statistical study of solar proton events (Melendez-Venancio et al 1998) based on more abundant SPE statistics than in previous works.…”