at a velocity Vo ~ 10 cm/sec. The electric field
induced in the vicinities of the singular point will turbulence the plasma in that region and trigger a durable and low-power flare process (Ramsey and Smith, 1965; Pustil'nik and Stasyuk, 1974). It is of great importance that this type of flares should result in a direct injection of weak fluxes of the accelerated particles into the solar wind along the force lines open into the wind. In other words, these are the 'weak proton' flares (see Fig. 4.18.2).
Comparison with observations shows that the realization of this type of flares is also fairly high, namely the weak flares with low-frequency bursts of type III are localized above the spots (Pustil'nik, 1976) and a considerable number of such flares give rise to faint bursts of solar CR in interplanetary space (Dorman and Miroshnichenko, M1968; Dorman, M1972, M1978; Miroshnichenko, M2001). Besides that, the kink-instability occurring in case of excessive twisting of the spots and the 'sporadic overheating' of the coronal condensation from under the low-lying prominence flare may be treated as the additional (non-evolutionary) ways of flare triggering.
Examine the situation taking place when a large spot of a new loop of the field (photospheres field S) appears in the penumbra. The X- type singular point with the depression of the upper open force lines over this point and the Y-type coronal singular point will appear in such region (see Fig. 4.18.3).
At the same time, the closed tubes of the upper field are also overheated, a coronal condensation with surface flute soothing is formed, and the chromosphere plasma leak into the force line depression. Similarly to the process described above, in Section 4.18.2, the overheating of the coronal plasma will result in the triggering of a flare in the upper corona. An accelerated particle flux will be ejected downwards from that region. When such flux reaches the field line depression above the X point, the centrifugal acceleration produced by the flux will make the plasma in the depression heavier and the system will turn out to be unstable with subsequent downward ejection of a flute with plasma, fast particles, and field. According to Pustil'nik (1977a), the total energetic of the coronal flares is quite sufficient for the above process to occur. As a result, a flare dissipation of the field will be triggered in the lower current sheet in the region of the strong field of the spot. Such flare is characterized by: (i) a high power owed to the strong field, (ii) the direct injection of intense fluxes of accelerated particles into the solar wind along the open force lines (see Fig. 4.18.3). In other words, this is the classical power proton flare.
All basic predictions bearing on this type of flares are actually realized in the observed proton flares; the proton flares occur in the region with magnetic geometry of type S (Dodson and Hedeman, 1964), they are characterized by a pre-flare phase (pre-burst) within 20-60 min before the main flare (Lincoln, M1973), and, finally, the study of the radio fluctuations before the proton flares has shown that the overwhelming majority of the proton flares observed were preceded by a strong wobbling of hourly radio fluctuations which began a day before the flare and caused, a 10^30-fold increase of the fluctuation amplitude by the moment of flare (Kobrin et al., 1975, 1978).
4.18.6. The problem of particle acceleration in the current layer of solar flares
According to Pustil'nik (1977b), the particle acceleration during anomalous dissipation of magnetic field is one of the most important processes in the problem of solar flares. The available observational data obtained by both direct measurements in the interplanetary space and indirect methods permit the following conclusions about the characteristics of accelerated particles to be drawn (Dorman and Miroshnichenko, M1968; Dorman, M1972): (i) the spectrum of the electron component is of the power form De (Ee E—Ye with exponent ye =2.5^4 and the most frequently realization lye} ~ 3; (ii) the spectrum of the proton-nuclear component is also of a power form with exponent Yp and an abrupt cut-off at energies Ep,cr from few up to 10^20 GeV; (iii) the chemical composition of the accelerated particles is similar to the chemical composition of the solar atmosphere.
According to the modern concepts, the flare energy is released in the turbulent current sheet where the high density of current j > necsi and the anomalously low conductivity result in a high power of the energy release in the course of magnetic field dissipation P ~ j2 /a*. The theoretical estimates of the power are in a good agreement with the observation data. The thickness of the sheet may be estimated
by equalizing the latest P ~ 10 erg/sec to the rate of the field processing in the sheet:
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